Who says a cartoon can't have heartwarming moments? Especially a cartoon as bizarre as Regular Show?
Despite everything, Muscle Man's relationship with Starla should count. Granted, every time the two of them make out is considered disturbing and disgusting by the show itself due to the fact that neither them is what you would call a looker, but they've consistently remained one of, if not the, longest standing couple in the entire show, and Muscle Man frequently goes to great lengths to make Starla happy just because he loves her that much.
Mordecai finally letting Rigby win at punchies in "Death Punchies," complete with a heartwarming scene where they soar out of the magma pit together.
"Dude, of course you can be Player 1."
From the hot dogs episode: "See, I told you I could fix this."
It's somewhat of an inverted moment of heartwarming, because it comes right after Rigby successfully puts the blame on Benson for something he didn't do.
Rigby's apology to Mordecai in "The Unicorns Have Got To Go", complete with big, sorrowful eyes. Mordecai forgiving him probably counts as well.
Skips thanking Mordecai and Rigby for throwing him a birthday party, because no one had ever thrown him one before.
From the "Don" episode: Mordecai telling Rigby that Rigby's like a brother to him, and that he still sticks with him even when annoyed by him... then Rigby finally caving in and giving Don some "sugar".
Benson has several, particularly in "Mordecai and the Rigbys" when he goes to see their performance simply to watch them fail. However after Mordecai and Rigby were getting booed on the stage for admitting to lip synching (albeit accidentally), Benson manages to get the audience cheering by immediately applauding for them instead. For the first time, he shows that he's not simply a Grumpy Bear who yells at them, but actually a Not So Stoic who's simply Not so Above It All.
Rigby thanking Mordecai for helping him get over his fear in "Ello Guvnnor".
At the end of the episode "It's Time", when Mordecai is sent back time after accidentally killing Rigby, he seems very happy to see him alive again
From the episode "Appreciation Day." Benson is handing out plaques to everyone and saying what they did to deserve their appreciation. He hands one to Pops, and says, "Pops- for helping a baby bird back into its nest." The scene wasn't shown, but the thought of sweet ol' Pops lovingly placing a baby bird back into its next is ridiculously adorable and heartwarming.
"Thank you, papa... thank you."
Leon pushing Benson out of the car so he can perform the Heroic Sacrifice himself.
The end of "Benson Be Gone" has Benson order Mordecai and Rigby to get back to work. They instead go play video games. Benson watches them leave from his rear view mirror and smiles in content. Given the hell he had to go through to save them from the workaholic demoness Susan, he not only understands their own feel of down time once in a while, but also is glad for things to return to normal.
Really, any time the Five-Man Band come together to accomplish something. Sure, they don't get along a good chunk of the time, but when they do, it's both a Heartwarming Moment and a Moment of Awesome. The best examples are in "Rage Against the Television", where the group performs a Misfit Mobilization Moment to help Mordecai and Rigby, and "This Is My Jam", where the others come to help defeat the physical manifestation of an Ear Worm, without even being asked.
Though to be fair, Mordecai and Rigby weren't the only ones that were plagued by the Ear Worm, they all were. Still counts that they'd help, though.
"Hey, Rigby? Do me a solid and come to the arcade with me."
It was Rigby's solid that nailed it down for This Troper. After being a total douche through his solid-abuse, he does the honorable thing and keeps his word by destroying the tape with no regrets.
He didn't even have to. He made up that thing about the solid so he'd have an excuse to destroy the tape without looking like a wuss.
"Really Real Wrestling": Pops apologizes to Benson and says that Mordecai and Rigby aren't to blame.
Skips putting his soul on the line to win Rigby's soul back from Death and apologizing to him for killing him (well as much as The Stoic can)
A combination of awesome and heartwarming: in "A Bunch of Baby Ducks", Mordecai and Rigby team up with a mother duck to go rescue her babies from a creepy old man.
"Hey, Mordecai and Rigby. Thanks... for being the coolest losers we know!"
Pretty much everything with Mordecai in "Skunked" while he's trying to cure Rigby from being a Wereskunk. This was really one of those episodes that shows the same thing Mordecai said in "Don", that he cares about Rigby like his brother.
Skips returning to bowl even though Death was holding a secret over his head that he felt could have ruined him, after looking through the scrapbook. Skips even referred to the guys as his friends and made it clear he'd never turn his back on them.
In the camping episode, the part where Margaret and Mordecai were lying on the hood of her car and talking was just so great. Their dialogue was unbelievably natural. It's one of those moments when you just want to track down the person who wrote the episode and give them a big ole hug.
Rigby actually being nice to Eileen for once (and her happiness at that fact) was pretty sweet, too.
Benson's admission near the end of "Cool Bikes". "Mordecai and Rigby . . . are the coolest guys I know."
He even saves them from getting sentenced to death for being too cool.
The entire rapping contest episode definately qualifies as this.
In a fridge heartwarming way, Pops getting a spare cake for the surprise birthday for Skips waaay back in season 1 when you watch the episode "Skips Vs Technology"'s opening montage of Skips being at the park when Pops' was just a kid.
The Reveal of what Mordecai and Rigby had been trying to print all day in "Skips VS Technology". A thank you note to Skips, for all his hard work around the park.
The montage at the beginning of the episode is also sweet. An ageless immortal and what Skips finds most fulfilling is helping the various generations of workers around the park.
In "Eggcellent", the fact that Even when Mordecai felt that Rigby may never recover, he still kept his promise and went though all the trouble to get Rigby that hat.
In a way, while also mostly a Tear Jerker , Mordecai punching Benson in the face for the crap he said. Rigby may have screwed up, and for a stupid reason, but Mordecai is NOT going to take shit from Benson on saying things like that about his best friend.
The entire Five-Man Band helping Mordecai so he can win said hat. Also, both the scene where Benson admits that claiming it was Mordecai's fault this happened was a really stupid thing to say and the later one where Mordecai tells Benson he didn't mean it when he said nobody likes him, and that even though Benson can be a jerk, he's also a good person, and that Mordecai really does consider him a friend. Seriously, this episode was heartwarming incarnate. Seems like there's one of these per season, 'Don' and 'It's Time' being the last two.
That small scene when Benson gives Mordecai a small smile and saying "Just get in there and win the stupid hat for Rigby." That was a really nice thing to say.
In "Gut Model": HFG telling Muscle Man that he would be miserable without him and he is his best friend.
Mordecai handing over entire stack of money he had been saving up for a date with Margaret when it becomes clear Rigby needed it to save his own life.
In "Busted Cart" Benson tries to reach a warehouse before the warranty on the busted golf cart (which, of course, Mordecai and Rigby busted) expires. He explicitly tells them not to come with him, but they sneak on board anyway out of a sense of guilt. Of course Benson freaks out... and then we get one of the sweetest moments in the series when Rigby asks why Benson hates them so much, and he gives a pretty nice speech about how he doesn't hate THEM, but some the things they do and all he wants is to push them to be better - implied to be "as good as he knows they can be". They then put on some music and drive along happily together. Of course, more stuff happens, they screw up more and Benson gets pissed again, but it's a very, very sweet scene and shows more of Benson's development as a character over the series.
The fact that Mordecai and Rigby risked their LIVES for Benson's job.
Both Mordecai and Rigby realizing that they really screwed things up when Benson has a complete emotional breakdown upon believing he's going to lose his job in "Broken Cart". And then putting their lives on the line to keep that from happening.
The ending of "Access Denied" itīs pretty heartwarming, with Mordecai and Margaret finally dancing with each other.
Also doubles as a hilarious moment, and YMMV, but Muscle Man as a little kid and his dad making "My Mom" (or "My Wife") jokes.
Heck, everything involving Muscle Man and his dad in that episode. Not to mention that Muscle Man honestly opens up to Mordecai and Rigby and admits they're his friends.
The revelation of why Skips always skips from "Diary". Apparently, some of his happiest moments were skipping with a past love, who he most likely outlived due to being Immortal. He skips all the time, as something to remember her by.
In the same episode, Rigby actually admits that Eileen would be hot if she changed to suit his tastes."
Muscle Man's concern for Pops, and the fact that he gave up pranking for him. Considering the fact that Muscle Man is the kind of guy who gets his kicks from hurting people, and once LAUGHED WHILE RIGBY WAS CHOKING, that was rather touching.
Mordecai and Margret's interactions in "Death Bear". And then there's the end when Mordecai tackles Death Bear to save Eileen's life.
There's also Margret telling Mordecai he was brave and Eileen telling Rigby that even though he wasn't, she still liked being with him.
Pops winning the blue ribbon (his 10th one!) in the pie contest.
In "Terror Tales of the Park II," Benson's concern for Pops. He knows that Pops is very child-like in nature and is utterly terrified of scary stories, so he constantly yells at the others to not tell scary stories, to avoid frightening Pops. Though everyone has a soft spot for Pops, it's most evident with Benson, because Benson usually isn't very gentle towards other people at all.
Pops insists (pathetically and unconvincingly) that he isn't scared, because he doesn't want to ruin the fun of the others.
Though Pops hadn't completed the milk challenge, the guys still would have let him join in on guys' night just because they saw how much he wanted it.
His addition to the scrapbook and his joyful giggling cements this as heartwarming.
Rigby thanking Eileen for her help in "One Pull Up". He would've hugged her if it wasn't for his massive muscles that he feared would crush her spine. She took her chance as she removed her glasses. Worth it.
All of "TGI Tuesday," especially the ending.
Mordecai and Rigby hanging out with the baby ducks at the end.
Before that, the mother duck scolding Benson for not just yelling at her babies but for also yelling at Mordecai and Rigby, which shows how much she appreciates them for taking care of her babies.
After the ducks lose their first fight with the geese, Mordecai and Rigby refuse to abandon them no matter how dangerous the situation is.
In "Fool Me Twice," when Mordecai and Rigby wants to give up on the obstacle course, Benson helps them continue despite not wanting to participate in the game show in the first place.
Mordecai and Margaret finally kissing at the end of "Picking up Margaret".
"Radio KILLIT" is pretty much a love letter to the days of the independent radio DJ, and as such is full of awesome and heartwarming moments. A great one is the flashback to the station's better days, with all the DJ's doing what they do best, and a Suspiciously Similar Song version of Rush's "Spirit of Radio" playing in the background.
In "Skips' Stress", after dealing with the Stress Monster, Pops' car has a flat. Skips prepares to fix it but the others tell him they can handle it and work together to fix it. Skips' smile says it all.
The whole episode is full of Heartwarming moments, really. Everyone at the park clearly loves and values Skips. When they realize he's too stressed to work, they give him the day off and take up the slack. And when that's not enough, they get him to the Stress Bell and stand with him while he battles the stress monsters.
"Trailer Trashed", Mordecai, speaking on the behalf of the other park gang, with probably the exception of Thomas, saying they consider Muscle Man a friend. Take in mind that in the beginning of the series Mordecai consider him annoying and to hear him say that show that when the chip are down they have each others back.
"Meteor Moves", Mordecai and Margaret finally get together after a cosmic being forces them into the Friend Zone.
At the end of "Country Club", Benson tells Mordecai and Rigby that he's proud of them for sticking up to the titular club and trying to get their things back.
Benson learning to trust Mordecai and Rigby in "Blind Trust." Especially at the end where they admit that they love each other.
The entire premise of "World's Best Boss." The workers going out of their way to get Benson the mug, their sincere compliments towards him while fighting the other boss' workers, and then Benson joining in on the brawl.
Despite it being more of a Tear Jerker, Margaret running out of the restaurant in tears after rejecting Mordecai shows how badly she feels about doing it to him, and that she would had gladly been his girlfriend if she hadn't been accepted to her dream college.
Rigby being fully and completely supportive of Mordecai throughout the entire episode. It shows just how far he's come from being the selfish jerk who tried to ruin Mordecai's chances of getting together with Margaret in the past. The ending scene with Rigby coming to comfort him on the roof after his heartbreaking rejection is beautifully touching.
Even if the ending makes it bittwersweet, it's hard not to smile at the "date montage" in the beginning, which plays this a bit more straight.
The entire park uniting to cheer Mordecai up at the beginning of "Laundry Woes" after his devastating breakup with Margaret, and the montage of them gradually succeding. It shows just how far all of them have come since the beginning of the series.
Mordecai letting Margeret go once and for all.
Towards the end of "A Skips in Time":
Walks: You are pretty cool... but I'm still not changing my name to Skips.
Skips: You will, you've just got to find the right girl.
Rigby: And Eileen worked really hard to help us! (Rigby and Eileen smile at each other)
And shortly afterward . . .
Pops: But that is the reason I consider you my best friends!
Don't forget the president of the company that makes the Tants, because after he sees this scene, he gives all of them free Tants after burning the fake ones, saying that real friends deserve real Tants.
In "Bank Shot": When Rigby is in trouble on a Bank Shot bet, his first reaction is to call up his brother Don.