A few of "Emma's Words of Wisdom" moments probably count.
Including "Emma's Words of Wisdom - AGAIN !" in "Kids React to Charlie Sheen".
The Eye Take of Morgan during the "le Internet Medley" video. She was laughing, and suddenly went "O_O what the heck?!" when the ALL YOUR BASE ARE BELONG TO US part barges in. Her expression is just priceless.
Morgan's "answer" to the question whether the video was real or fake during the "Kids React To Greatest Freak Out Ever" video.
Also don't forget her very nonchalant "This boy's a train wreck." in the same video.
Morgan's Random Animal Sing-a-Long from the Keyboard Cat video.
The kids then trying to replicate what Gollum sounds like:
Benny Fine: What does Gollum sound like? Everhet(flapping his hands together): Precious! Elle: My precious! Seth(whispering tone): My precious! Troy(looks towards the camera, also quiet-sounding): I don't want to see The Hobbit! Cooper(wiggles fingers): My precious! (Benny giggles, Rafi says "Ah!" in amusement, then Cooper repeats)
Emma R. reacting with sheer horror at that one screencap.
There's just something weird about Benny Fine sticking to the the cards, to the extent that one particularly elaborate question is being fielded by four-year-old Cooper.
Benny Fine: Some people think there's a lot of deep meaning and messages hidden throughout this video. Other people say that no, it's just random. What do you think? Cooper: (possibly latching onto the last thing she heard) I think it's just random.
In the middle of the video, Jake randomly asks why the puppets are British.
In Kids React to Gay Marriage, while it's a more serious topic, most of the kids don't understand what's going on at the beginning, but Maksim, one of the youngest, just says matter-of-factly, "So they're gay?" It's funny how sometimes the youngest kids know the most.
The Fine Bros: What did both of those videos have happen in them?
Maxim: Justin Bieber married a guy...
The Fine Bros: That wasn't Justin Bieber!
During "Kids React to Rhett & Link", the kids are asked to do come up with something to say before they did something stupid that led to their death.
Derek:A Weeping Angel! Hold on, let me rub my eyes. (Benny and Rafi crack up off-camera)
During the reaction video on Disney's Frozen - "Let It Go" (Multilanguage), Lucas immediately took off his cap once Elsa began to sing.
I guess so as long as he wasn't like "Come inside." (does creepy funny face) (imitates Salad Finger's voice) Can I have your rusty pen? Eric: It's like they took my diary and put it in videos!
Appropriately enough their first episode in October, "Teens React to Slender" is filled with these. One particular moment is Kostas getting excited over finding the first page, so much so he jumps out and hits the microphone, and only milliseconds after apologizing he gets caught.
Snap-polls are a recurring thing across the React series. The one here starts with a landslide vote against child pageants; then Lia feels merely iffy about her vote, and the numbers update in fractions. And then Rumor, who's admitted to Bile Fascination with the show, causes the fractions to balance out.
The same thing happened in the Bill Gates vs. Steve Jobs poll. Ethan said he was torn because he uses a Mac but prefers a PC, so his vote caused the poll to also be updated in fractions, only for Rachel to immediately have her own indecision because she said she'd love to work for either Apple or Microsoft, so the fractions evened back out.
Rumor: You guys actually found something I don't like!
The Mondegreens of "Gangnam Style", capped by Isaac with "Open condom store?"
And earlier, Rachel cutting herself off mid-sentence when the toilet scene pops up, followed by her reaction after the video ends (made funnier by the trepidation in her voice): "Hi guys, how was your day?"
Subverted, though, since Tay does clarify that he's grateful for the success the song has given him and doesn't seem to regret it in the least, aside from a passing mention of a "love/hate relationship" with it.
Episode three ("YouTubers React to Rewind YouTube Style"): That awkward moment when MysteryGuitarMan realized that "Rewind YouTube Style" and YouTubers React were Not So Different.
Brittany and Wong Fu Productions both panicking as they realize they're about to be rickrolled again.
The Fine Bros doing their own spin on the Goat remixes in Episode 6... with the YouTubers.
Everybody's horrified reactions in Episode 7 to the Knife Game song.
At one point, Benny and Rafi offer their guests the chance to do it. Most people choose not to, apart from Tay who "cheats" by pointing the knife the wrong way up, and Shane moves to do it, prompting a horrified "no" from offscreen as they think he actually will. Jordan Maron actually lampshades the fact nobody wants to do it as well.
"YouTubers React to Japanese Commercials". The commercials are indeed funny themselves, but Hannah Hart compares her efforts dating girls to one of them, while Felix recommends that the creators of the commercials go into horror games. At one point for one of the commercials, Harley just remarks, "I don't wanna sound racist... but, how very Asian."
Some of the individual reactions are gold. Especially the ones to the Tarako spaghetti sauce ad, which features a small doll ominously rotating in front of a mortified child:
A large group of them just imitate the look of utter terror on the little girl's face.
Shane Dawson: Have you seen my videos?! I could do this in my sleep!
"Try Not To Laugh Challenge": Aside from the various stars bursting into laughter, which can be quite contagious, there are moments where you can tell the people are taking the challenge literally. Captain Sparklez's reaction to the Ladder Goat being murdered is simply "Poor goat. He didn't deserve that". He also has an adorkable moment where he's made it through the challenge and simply goes "not funny".
Hank Green mistaking the guy who did ladder goat for Pew Die Pie. Then he finds out that he gave in and laughed because he made the mistake, something which is essentially treated as an Epic Fail.
In the bonus footage, Shane Dawson essentially has a Rage Quit from watching the entire thing again when he forcibly bursts into laughter and keeps thrusting in time with the Stormtrooper air humping, begging to stop.
"Rejected": The video starts with Smosh squeeing out over the titular animation alongside Timothy Delaghetto, which sets the tone for the whole video. Then we cut to the second animation and Ingrid and Olga's horrified reactions at the guy growing an extra head.
"MY ANUS IS BLEEDING". Again, Harley is laughing himself silly alongside Philip De Franco, whereas Tay deadpans "he needs to see a cloud doctor" and Felix simply comments "I guess it's that time of the month again". When later asked what was happening to the cloud, Tay comments "I didn't learn that in meteorology".
Hank notes the lampshaded Sanity Slippage of the cartoons, commenting that he felt there was no sanity in the whole thing to begin with.
"YouTubers React to Vines". Shane Dawson of all people thinks that Everybody Spurts is gross. Tay Zonday just comments that the people doing it need to see doctors, and Jordan Maron mistakes it for the REM Vampire meme (which doesn't exist).
Joe Bereta and Elliot Morgan then start having a mock argument as to whether or not the other is giving good advice to people starting out on Vine.
At the end of the video, everybody does an "Everybody Hurts" style clip. Each one is fantastic. Special mention must go to Jordan's and Shane's, however, as Jordan is seen doing it with a towel over him (te only one to do so) and Shane tries doing it with mayonnaise but can't even do it for the 7 seconds a Vine video would take as he finds it so disgusting.
The bonus video for it has Jordan reacting to Ryan Gosling Won't Eat His Cereal by saying "he doesn't want it, stop trying to feed it to him", after the titular protagonist throws it into a bookshelf.
Tay describing Vine as a 6 second version of Popeye.
The bonus reactions expand on the "Everybody Spurts", where Phil can't keep doing it because it's just too funny, Ryan Higa can't keep it down because the liquid he's using is really cold, Tay does a disturbing Slasher Smile, Ingrid is unable to stop herself laughing, Jordan also can't stop himself laughing and you can hear Benny and Rafi laughing from offscreen, and Shane squirts an entire thing of mayonnaise in his mouth.
"K Pop" (aka "Korean Korean Korean 'fantastic, baby' Korean Korean Korean.") Trisha and Meg squeeing out over the K Pop videos. This is followed by Ian and Anthony both dancing along, only for Anthony to randomly start rubbing his nipples, then in the next reaction Anthony asks if he's seen one of the girls in Psy's videos, at which point Ian says "No, you're just being racist"... then quickly wonders if Anthony is in fact right.note The girls in each of Psy's videos are in other Korean girl groups, and not in Girls' Generation. In the third one, Tay obviously cannot take the boyband serious and starts making up fake lyrics.
The various Mondegreen moments that people have throughout. In the Girls' Generation video, Anthony wonders if they are singing "I got a boy on my chin", then can't keep himself from laughing every time the line comes up. Tay doesn't dare to guess, just commenting "I need Google Translate".
When asked what she thought of the first video, Rosanna just says "Fap fap fap fap fap", and again for the third video.
DeStorm noting the three Porsche cars in the background of the last video, telling Rick Ross that he had better watch out.
"YouTubers React to One Direction's Best Song Ever". Throughout the video, it's obvious that Mark and Todd from Barely Political consider the entire video to be torture. There are so many thinly veiled insults towards the band too.
"YouTubers React to Farting Preacher," especially the end where the Fine Bros put fart noises over everyone, even those who didn't consent to it.
Zoella: "I would hope that [the Farting Preacher] would have a sense of humor and find them funny. I think if somebody did that to me, I would find it hilarious." (fart noise)
Philip DeFranco's reaction to being told that the preacher was a televangelist during the 80's and 90's.
Philip: "So question, before you finish it; did he die of a drug overdose, or did he go bankrupt?"
Benny: (brief pause) "He didn't die, but he was in courts for stealing all these people's money."
Philip: (sarcastic) "What? I am so surprised."
And then right after that:
Benny: "But he lives on forever as the Farting Preacher."
Catherine: (busts out laughing, in between laughs) "He wanted so much more out of life! And he's just the Farting Preacher!"
Philip: "Wait, are you doing it, are you doing it?" (brief pause) "Why are you smiling like that? Did you do it?"
Jack and Finn: "Here we go! I knew this was going to come up!"
Catherine: "Hey guys." (gradually lifting one leg, punctuating it for fart noises to be inserted) "Look — how — mature — we are — uuh!!"
They even did an entire video filled with fart noises, in the style of the source video. The farts serve to bleep out swearwords, play over the title sequence, and randomly pop in over random words that people are saying.
The Fine Bros.: "What is your advice for someone trying to promote something on YouTube? What is the best way to go about it?"
Kalel: "I would say... boobs." (Anthony bursts out laughing)
YouTubers React to Bunnies Can Fly...Proof:
Question: "What do you think they said to their daughter once the camera turned off?"
Harley: "I would go right to the library and get one of those big white books, you know one of those awesome white books that has all the pictures, and just get the bird one. I'd be like 'You see how cute these birds are? They need to obliterate things like that bunny to live. You want the birds to die? No you don't. So the bunnies must die.'"
When Catienote aka Boxxy is about to cry trying to explain Kiwi, she looks offscreen and we get this gem.
Catie: Oh, I found tissues.
In the bonus video for the Short Viral Videos episode, iJustine has an insane fit of laughter watching "Go! BWAAH" and "Sneezing Baby Panda". How do the Fine Bros help her calm down? By showing her "Go! BWAAH" again. Her face is just priceless.
Benny: "Do you have any idea who those two guys are?" Series of kids: "No. No. Nope. No. No. No. No." [shot of Anthony watching, his face slipping further and further into a sad pout with every "No"] Zak: "I think they're Smosh?" [Anthony's face immediately lights up]
Kids React at the Daytime Emmy awards. The kids get in line and announce their age, presumably for archiving - Jake is 12, one of the twins calls out 11, Elle says 10, and Dylan is nearly Pavlov'd into saying 9 (should be 10).