Perhaps the show's concept itself, two friends playing video games together and the internet having a good time watching them have a good time.
In the 20th episode of Pokemon Emerald, Jon takes a picture of him and Ego relaxing on the couch. As they're talking about sharing it over twitter, it pops up on screen. The picture looks exactly like a picture you'd find on anyone's Facebook or Twitter: Two Gamers on a Couch, hanging out and smiling.
In the Aladdin finale, Jon and Arin can't stop talking about how beautiful the carpet ride bonus stage is, even singing along with "A Whole New World". It's actually kind of sweet.
In Kirby's Return to Dream Land Episode 2:
Jon: Is that Arin and Jon agreeing on something? What is that shit?
Ego: It's really strange how often we disagree.
Jon: Yeah, but it's funny. I remember when we were first starting Game Grumps, cos I was like worried, I was like "Do you think we're ever gonna like fight or y'know disagree" and it was like "Naw. We argue a lot, but it doesn't affect our friendship." And I was like "Yeah, I guess you're right." We argue SO MUCH and it's always like "Awesome! I'm glad you feel that way. Come over next time?"
Near the end of Super Mario Land:
Jon: You've never once lied to me in my life.
Ego: *sigh* I did. I did once. When I said I hated you.
It is just kind of heartwarming seeing that despite how young the project really is, the fanbase for the Game Grumps is strong and wonderful (with the large amounts of cool remixes, animations, etc.) to the point where Grumps and fans alike call it "the best fanbase ever".
The finale to Kirby Super Star was pretty nice, with Jon talking about how they just finished their first game, how far they've come with Game Grumps, how great the fans are, and how it's really made the two of them best friends.
During part 2 of Wild Guns, Jon comments that he hasn't seen Arin have this much fun playing a game in a while. Considering whatgames they have been playing lately, this might not be too far from the truth.
At one point during their Magfest panel, one fan wanted to ask Barry a question. Jon took out his phone and called up Barry, and when Barry answered, Jon just said, "Hey man, you're live at the Game Grumps panel!" and the crowd went NUTS! A massive cheer was sent up and there was a "BARRY! BARRY! BARRY!" chant. When the noise died down, Jon asked if Barry was still there, to which he responded with a choked up, bordering on Tears of Joy "Yeah!"
At Magfest 2014, Danny outright stated that without Barry, Game Grumps wouldn't even exist.
The fact that the fandom loves Barry so much and everyone involved in Game Grumps fully appreciates him for his vital role in producing game grumps.
Jon berating Arin when he insisted on clarifying that Jon went to get him Powerade because he was too sick to do it himself.
Jon: I'm gonna pause this... Are you fucking implying that you w- of COURSE you were too sick to get it! It's not like you were being a douchebag, what? I would've asked you for fucking SEVEN Powerades!!!
Any time Jon squees over something in a game. While both of the Grumps love games with all their heart and souls, whenever Jon encounters a good one (or at least one with something he enjoys) his happiness comes across completely. One of the best examples of this is the first episode of Kirby's Return to Dream Land where Jon (and Arin) is barely able to contain his joy to play what he considers an excellent addition to an already excellent series.
Jon: "Do you just see a girl you wanna marry, because I'm worried for you if you're walking around being all like, 'I wanna marry her!'"
Arin: "No, not in public, in my house! Because she lives with me."
Jon: "[giggling] Awww, that's even cuter, stop it!"
From another Sonic episode...
Arin: I don't really care anyway, I was just filling time.
Jon: BAPADABOOP BOOP BEEP- What do you mean 'filling time'? I'm not good enough to be time alone? I-I can't be your time? You have to fill the time with me?
Arin: Uh yeah...I have a good time when I'm with you.
Jon: *Laughs happily.*
From Sonic '06, Jon actually having fun as Blaze. He even compliments her, saying she's cute and reminds him of Dot.
From yet another Sonic '06 episode (75 to be precise): Jon storms out of the room while Arin makes noises, and "fires" Barry. But when he's coming back, Jon is apparently asked by Barry if he was serious, and the mic picked up his reply. It's a silly moment but sweet at the same time.
Also the way Jon asks Barry to add that extra scene in at the end of the video is also pretty heartwarming.
Near the end of Mario Party 2 Revengeance Part 6, Arin makes a joke about calling a "Side-kick rental" service and asking to refund Jon and replace him. When Jon tells him that he heard the whole thing, Arin says he was talking to his karate instructor, who taught him how to "side kick". By the end, after a high five, Jon says something about hurting the ones you love without realizing, to which Arin responds by calling side-kick rental back up to say he didn't mean what he said. Jon still gets upset at him for lying though.
In Sonic 06 part 78, Jon gets a call from his mother, who he puts on speakerphone for the audience. She called him to tell him his father survived a dentist operation, and acted really shy when told she was on the show. The entire exchange is filled with adorable. In a bit of Meta-heartwarming, the fans seem to have taken a liking to her, calling her MomTron.
The entire Grant Kirkhope episode is one. You can tell Jon is in awe of being in the presence of one of his idols.
In Sonic 06 part 85, after getting their sweet revenge on Sonic as Silver (Complete with evil laughing from Arin) they agree that the whole channel was worth it because of the friendship they've forged through it.
The epiphany in Donkey Kong Country 2, part 6. It's interrupted by an in-game death and the two proceed to joke about humiliating themselves for others' enjoyment, but what Jon said was completely sincere.
Jon: "You know what's the compliment that we get about our, like, fanmail or whatever that makes me the happiest every time I see it?"
Arin: "What's that?"
Jon: "It's when people are like: "Fuckin... Whenever my day sucks, I watch Game Grumps and it's better." And I'm like... There is a reason to do this."
During Magfest, Jon and Arin try to recall how they became such good friends. Their first meeting is described as Arin answering the door with a plate of cookies and Jon standing outside with a pack of Dr Pepper. It is a sweet moment.
Jon's heartfelt thanks and appreciation towards the show's viewers in his retirement announcement.
Any moment, especially in Super Mario Bros. 2, Mega Man 2 or Jackal, where Dan makes Arin burst into uncontrollable laughter. While it's sad that Jon left the show, it's clear that Arin and Dan's friendship is just as strong.
The fanimator GregzillaGT made an animation that was intended as a brief tribute to the end of Jon's run on the show. After going through some of his funny moments, the final scene shows Jon leaving on a gigantic Jacques, the others looking on sadly (Arin especially). The very end has Jon outstretching a hand so Arin can high-five it right before leaving, all set to a melancholy orchestral remix of "Pause Balls".
During The Legend of Zelda run, Danny takes a moment to ask Arin if he's got any messages along the lines of "Game Grumps saved my life". He confirms that not only have they got messages like that, they've got messages about how people have got into relationships through being fans of the show and wearing the merchandise in public, causing someone else to recognise it and strike up a conversation...
Also during The Legend of Zelda run, Dan tells a few stories involving his dad. The only one where he doesn't do an impression of him with a silly accent is when he talks about when his dad quit smoking.
Arin's story afterwards recounts his friend from when he worked at Blockbuster who had been a heavy smoker until she found out she was pregnant.
So far, most of their Kirby's Epic Yarn playthrough consists of Arin and Danny acting extremely cheerful and squeeing at everything in sight. They claim that it's impossible to be grumpy when they're playing it.
In Part 4 of the Super Castlevania IV playthrough, Suzy stops by to give Danny some tea, at first the Grumps are all hammy and then sincerely appreciate Suzy stopping by.
In Part 9 of Kirby's Epic Yarn, Danny recounts a story about his grandparents' wildly differing opinions on coarse language, but then mentions how they were together for 62 years. He then comments Arin and Suzy are the same, to which Arin says 'I hope so.'
Their project of selling their game copies on Ebay sent to the Grumps raised 7,000 dollars towards Childs Play. Their appreciation for the fans is truly heartwarming.
The inclusion of Barry and Suzy when doing multiplayer games with at least four people on Steam Rolled makes it feel like they're all one big family.
Speaking of Suzy, her character is Suzy the Outlaw. Aww, she's a criminal just like her husband, Arin the Bandit.
F.L.U.D.D.'s apparent death during the Super Mario Sunshine finale leaves the two appropriately shocked as they believe it to be the end. After which they are appropriately relieved at the sight of it still being functional.
In one episode of Super Mario Bros. 3 Danny and Arin talk about the uncomfortable factor of becoming well known that it can be risky because it becomes harder to tell who is being nice and who just wants something from them. Arin admits he doesn't have that problem, it sort of helps his confidence but he knows Suzy loves him since she was talking to him before he became Egoraptor. Suzy loves Arin Hanson the artist not Egoraptor the Awesome series guy.
The Amazing Frog? one-off is both funny and this during the fight over the crown at the end. Arin and Danny are having so much fun just dicking around that it spreads to the viewer, who is likely laughing as hard as they are.
A real life example, but as of October 25th, 2013, Arin and Suzy finally married.
There's quite a bit of sadness involved by for the first time ever Danny tells the story of his depression, learning he has OCD and over coming it. It can be found here. The entire episode is worth watching. Arin is incredibly supportive of Danny.
That's not even discussing the fact that Danny discusses it because of all of the people willing to share their stories with the Game Grumps about their own struggles. He felt like he needed to pay it back to them.
Part 26 follows up on this at the very end, as Dan thanks everyone for their support and letters and stuff (and reminds them not to throw away their meds like he did, and to actually talk to a doctor about getting off them).
And on the less heavy side is that Arin and Danny both hate the term 'aspiring artist' and declare that if you write/draw/paint/create music ect. then published or put out or whatever then you're already an artist.
Part 29 of the Kirby's Epic Yarn playthrough. Dan brings up his Bar Mitzvah in Israel and how proud of himself he felt after getting through it. Also it was one of the few times he and his Israeli grandfather were particularly close, due to the living distance between the two of them.
The Epic Yarn finale reaffirms just how damn happy and adorable the game is. Danny can barely contain himself at the end.
During the Wind Waker run, Danny tells the stories of how his parents and grandparents met. Both of which are adorable.
Also, Danny and Arin reacting with horror and dismay when Aryll gets kidnapped, and Danny explaining during the Forsaken Fortress that "sister-stuff" always gets to him in games, because he loves his sis. Aww!
Adding to that, they are genuinely happy when Aryll and Buttlet are reunited.
Danny's wonderful story about recovering from psychological association problems.
During the Hello Kitty Seasons game, Danny points out that Arin designed their character to look like Suzy, something Arin wasn't even aware of.
The 2014 Magfest panel has a few moments. One about the Windwaker episode of Danny revealing his history of depression talking about that subject lead to a longer than usual applause from the audience. The other is that Danny makes a very special recording for his 3 year old nephew Nash and thus he has the whole audience sing with him.
If Arin's word is to be believed, Jon hugged it out with him and Danny during the festival. If nothing else, this helped give some comfort to those that were worried about their relationship since Jon left the group and if/how he'd interact with them during Magfest.
Arin and Danny turning into fans of Hayley Westenra is pretty adorable, even if it's intercut with their typically crass humor.
A minor one, but the fact that they (unintentionally) managed to get Shattered Memories' good ending.
It's a bit minor, but the Smash Cut style of episode endings usually happen mid-sentence (or mid-scream, occasionally). However, recently, the endings have more often ended with just Arin and Danny laughing together (with the Smash Cut in the middle of their laughter). It just seems like the two really like playing games and hanging out together and have a lot of fun, which is quite sweet.
In the finale of Super Metroid, when they are about to get killed by Mother Brain, they seem to honestly care about the Baby Metroid as it comes in to save them and when the Metroid dies, they seem honestly heartbroken when it dies. It makes the following fight all the more awesome.
In Part 13 of Katamari Damacy, Danny recalls his first day of nursery school. Mixed with Tear Jerker, he remembers how when he said goodbye to his mom for the first time, he was so sad, he cried behind the piano. And despite making friends with the teacher, and given blocks to play with, he was so scared of his new surroundings, he threw them at other kids. Adorably hilarious.
Their playthrough of The Adventures of Tom Sawyer. At first, Arin's unsure of the game, but plays along to share with Danny his love of the game. By the end, Danny sees Arin's fallen kinda in love with it, wanting to play more past the half hour.
When the Grumps' Night Trap playthrough comes to a premature end after they miss a button prompt, costing one of the girls' lives, they end up making their own ending. While also incredibly funny, they also make sure to RESCUE the girl, and Danny as the lieutenant gives a thumbs up and says good job for just barely saving her. Awwwwwww.
In Part 4 of Pokémon FireRed, we hear three quick stories about how Danny & Arin got along with insects. A little funny, but also heart warming in how they loved animals then as they do now.
The beginning of the Valentine's Day episode of Game Grumps fittingly titled Date Grumps
Danny & Barry using Single Train to celebrate Single's Awareness Day with other single grumps & grumpettes.
At the end of the Sheep Vs. episode, Danny interjects with a short plug for his favorite Ninja Sex Party music video. Halfway through the plug, Danny calls attention to Arin and Suzy's cat Mimi on the couch next to him. He then proceeds to melt from the Cuteness Proximity, fake-threatens to kill Mimi if the viewer doesn't watch the music video, and finally gives an adorable half-sob and says, "Oh, God, I love you, Mimi." His Kind Hearted Cat Lover side is unbelievably cute.
In Episode 26 of Pokémon Fire Red, Arin and Danny high-five and Arin's ring hurts Danny's hand. What does Arin do? He kisses Danny's hand. Aww!
Also from this episode, Arin's surprise & pleasure learning from Danny Luigi's Ballad has gotten 5 million hits.
In Episode 9 of Shadow of the Colossus, Arin admits that he'd do the same as the game's protagonist to bring Suzy back to life if she were to die. In other words, willingly search for, climb, and kill sixteen seemingly innocent monsters large enough to barely register him as an insect.note He also mentions that he'd definitely cop a feel while she was dead, but she'd probably be okay with it so that's besides the point.
Danny feels genuinely bad about killing several of the Colossi.
Danny becomes honestly upset after watching Agro fall to her death, and Arin admits that he felt the same way when he first played the game.
Danny & Arin okay with Polygrumps, because it pleases their fan-base.
Arin & Danny are friendly with other Let's Players, like Markiplier & Pewdiepie.
In one episode of Super Mario Sunshine, Arin and Danny talk about getting emails and letters from fans, and mentioning how a lot of them have fans starting them off by apologising for bothering them, then assuring viewers they don't need to apologise, because the Grumps like receiving mail from fans. Aw!
To clarify, they started arguing over what the name of the 27th President of the United States isnote it's William Howard Taft, btw. At one point, Arin realizes his "device" isn't in the room so he can look it up, so Danny offers to get up and get it, telling Arin to tell the audience a story in the meanwhile. And then we get the above. And the second Danny walks back in, Arin snaps back, acting as if that didn't happen.
Although it's in their typical joking-around style, Arin and Danny agreeing that Betty White is awesome, then talking about how "Pussy Up!" should be their new rallying-cry, against using "pussy" as a derogatory statement.
While doubling as a Tear Jerker, the reason why the Grumps are playing through "Kirby's Dream Course" is because after "[going] all out" on recording "Pokemon Fire Red" they lost the footage and Arin needed cheering up.
Episode 55 of Pokemon Fire Red is the first episode of Game Grumps that takes place after Danny's trip to New Zealand. He says that while he was there, he met a lot of fans on the streets, many of whom were pleasantly shocked to see him there.
During the same episode:
Danny: [laughing at one of Arin's jokes] I've missed you.
Arin and Danny start genuinely getting into customising their avatar for "Disney Princess", laughing about it the whole time.
While played for laughs, their surprise that Jodi Benson didn't become a hugely in-demand voice actress after The Little Mermaid is a sweet recognition of her talent.
Arin refers to Cinderella as Cillerenda at one point. It's nice to see that even though Jon left, certain things he said have indeed stuck with Arin. He did say, after all, that he would ask people at Disneyland where the closest Cillerenda Castle is "from now on until doomsday."
In the second episode of Gunsmoke Arin massages Danny's hand after some nasty button smashing, thanks Barry.
Arin and Danny giggling happily when they finally evolve Fuck King into a Vileplume.