Newest addition Stealth Bastard, it slowly builds up with TB's admitted ineptitude at platformers, then it culminates in the last minute.
In the Terraria collab, Jesse being the whitest guy TB knows:
Jesse: I got jumps now! I got jumps. Is that what the kids say? "I got the jumps"? TB: "I got—" no, that sounds like a euphemism for Parkinson's Disease.
Plus part 11, when during the blood moon, TB and Jesse kill a Top Hat Zombie, hoping to gain its hat for TB, something he desperately wants. TB dies in the attempt, and Jesse steals the hat as TB wonders where it's gone... Until it appears on Jesse's head. Hilarity Ensues.
Made even funnier if you noticed that Jesse wore the hat on the way there, and was dropping hints that he had the hat. Total Biscuit still failed to notice, until Jesse took out a torch allowing him to actually see him.
In a later episode (also involving a floating island, but a different one), Jesse tries to kill TB with fall damage. When TB explains that he no longer takes fall damage (due to a lucky horseshoe), Jesse forces him to demonstrate this. By mining the blocks directly underneath TB. Whilst standing on the exact same spot. TB didn't take fall damage, but Jesse was not as lucky.
In part 22, in a striking example of them actually aiding each other, TB finds a wooden boomerang and helpfully tosses it to Jesse... accidentally throwing it down the 1500+ ft. deep hellevator.
TB: We really should put guard-rails on that thing.
In Part 7, TB tries to sing the Terraria background music, but ends up singing a completely different song:
Total Biscuit: Wait a minute, that's Nyan Cat. AH! It's infected my head!
Also, when Jesse tried to kill TB with dynamite and blew himself up instead:
Total Biscuit: So what was in that chest? Jesse: Oh just a bunch of this stuff. *throws dynamite at TB* Total Biscuit: Oh, dynamite ... Wait, what?! *TB steps aside, but Jesse doesn't, followed by a big BOOM*
Similar incident to the above, still involving an explosion, with Jesse and TB trying to clear out the cacti in a desert biome. While Jesse's busy throwing bombs, TB quickly sets up a box around him, trapping him in with a bomb he just threw. However, TB didn't predict that he'd get trapped in the box too due to a glitch. There's a brief second of both of them panicking before the bomb goes off--which somehow kills only Jesse.
First one, TB has just returned from the Jungle area, with 2 Life Hearts for Jesse (as TB has used more already). TB proclaims his wonderful bounty, then accidentally uses one on himself.
Second one is when he places down the other fruits of their jungle exploits, in which Jesse died many, many times: two statues. Jesse becomes quite upset. And almost begins to sound like Cave Johnson from Portal.
TB repeatedly killing Jesse as punishment for his ineptitude by placing blocks in the hellevator. Never gets old.
In the Dead Rising 2: Off the Record collab, Jesse puts on the flattering crop top and short shorts ensemble and shows it off to TB. TB pauses, goes silent, and turns the camera around for a bit--before he turns around and smacks Jesse in the face with a lead pipe.
Ironically, that exact same outfit was previously worn by TB in his "WTF is..." of the title to emphasize the fun and sillyness he personally enjoyed. When Jesse starts prancing about and showing off the outfit to TB, TB said that there was something wrong with him.
Tons in the Magicka Let's Play with the Yogcast.
One example would be when they summoned meteor shower for the first time, not knowing what was going to happen and the subsequent panicking.
Simon:(after being told he is going to be the bait and walking up to the giant worm boss) "Hello. Nice to meet you worm! How are you doing? How are you this time of year? Are you well? Have you thought of letting Jesus into you-AAAHH!"
HQ: This ain't no sightseeing tour, 14. Get your butts on board- TB: BUTTS??!! Oooohhhh, WHO WROTE THIS SCRIPT?! As a British person, this makes me get VERY ANGRY!
Made even better if (as suggested by a youtube comment) you pretend that Jesse Cox is controlling the other bear driver.
Around 7:10 of his "WTFree is..." video of Nitronic Rush, things get incredibly...silly.
Even funnier is the fact that the trick system encourages things like this.
The Yogscast and TotalBiscuit ruin Trine 2: Part 2. (Only seen on their YouTube Re-upload, and not on the livestream itself, because they use Lewis' recording of the event and not TB's which is the YouTube video.) When they begin, Lewis and Simon tab out to read the multitudes of Donors for their charity, leaving TB with 8 minutes of air-time with the Yogscast's characters (the Thief and Knight) standing there. TB (Wizard) passes the time by pushing Simon (Knight) all the way under a leaf ledge, collecting boxes and rocks and beehives in the immediate area to literally bury Simon in junk and his own conjured boxes, once in a while commenting with the Yogscast to keep suspicion down. When he's done, in-game he types in 'Simon's New House' and for the rest of the unsupervised minutes, he makes his character 'dance' while waiting for them to come back. Hilarity Ensues when they find out, complete with Lampshade Hanging and Ironic Echo from their Magicka days (Hello, do you like bees?).
The last video of the year 2011 is his thank you to all his voters as he had won King of the Web. Though he doesn't do anything funny, there's something about his flowery pink teapot pouring tea into a Murloc tankard while listening to metal that sets you off.
WTF Is...Snuggletruck From wondering where his career has gone to pointing out how little sense the game makes, this video is 10 minutes of hilarity.
TB getting so mad on twitter that his wife decides to change his twitter password to stop him from raging. The next 10 minutes consisted of twitter banter between him and his wife as he keeps finding ways to access his twitter with her promptly disabling said access, and eventually taking over his twitter temporarily.
Genna Bain: *Whistles* Just another Thursday... changing @Total Biscuit's twitter password. TotalBiscuit: Hah, @GennaBain It won't work, I have access to the API! THE APIIIIII!!!!!! Genna Bain: omg, I have access to the INTERNET. *Disconnects @TotalBiscuit's internet cable* Genna Bain: Apparently he's off to get his phone now. Since I pay the bill... hrmmm I guess I could just disconnect it too huh? TotalBiscuit: Bah, she has pulled my internet cord. Little does she know about my 4G tethering! Genna Bain: @TotalBiscuit I know about your 4G tethering because I bought that phone you dolt. Knowledge, use it. Genna Bain: Oh and btw @TotalBiscuit those API settings? Yeah, I revoked them and changed your password. Now behave before I let the fanbois eat you! TotalBiscuit: Hello everyone. Cynical wife @GennaBain here. I have banned my husband from twitter temporarily because kittens and rainbows. That is all. TotalBiscuit: Halp halp! I'm trapped in another dimension. It is warm here and moderately sunny. #freetb