Any of the fanimation highlights from their Hat Chat podcast, but special mention goes to this one.
Episode 5 of their second XBLA Minecraftplaythrough: Ross accidentally sets their house on fire with a bucket of lava, and traps them all inside as they constantly respawn. You probably saw it coming too.
Trials Episode 55: The game has glitched out to the point where Alsmiffy and Ross can only crawl around on the map while Trott bikes through the course. They decide to just let Trott play through the course anyway, and we get this quote from Ross while Trott admires the course, "I'm glad you're having a good time. I'm dead on the floor, writhing around, trying to reach a tree checkpoint, Trott."
A few minutes after that quote, Trott manages to finish the match, while Ross laments "I didn't make it to the rock that I wanted to reach."
The end of From Ashes. Trott starts in the army base with no one in sight. He looks for the others outside and sees them on top of a mountain in the distance. Ross and Alsmiffy enter and pilot a helicopter over the island that killed the trio so much. They blow the entire island up. With Trott still on it.
Worms Clan Wars: Waterpack Woes, during sudden death (where every worm has one health only), Smith uses a waterpack, with his last worm, to shove one of Trott's worms into the water, and then attempts to move in on Trott's other worm, but goes too high when the waterpack runs out... And dies from the fall damage, taking Smith out of the game. Smith then proceeded to scream "shit" at the top of his lungs. Which was then repeated in slow-mo, courtesy of Trott.
Worms Clan Wars: Banana Balls Up, the end of the match features what is arguably the BIGGEST Chris Trott Error in their Worms playing history so far. Trott manages to get both of Ross's and Smith's last worms of the game in a position where they will drown within the next turn, winning him the game. Instead of just waiting for the turn to end and the two to drown, Trott takes out a Banana Bomb and, with a very careless throw, kills both himself and Smith, winning Ross the game. Their reactions are hilarious.
During their first livestream on the Dwarven Dairy Drive, they decide to play GTA, going through some mishaps. What sells the video is when Sparkles* gives the Sirs auto-tune, prompting them to promptly abuse it.
In The Walls 3: Aztec, the trio decide to build a tower to provide themselves a sniping position, and extend it outwards while they wait. While this does ensure their victory, from the perspective of the other groups, they're unknowingly building a giant penis in the sky, much to their amusement.
Smiffy discovered a certain something in episode #68 of Feed the Beast. After looking through the item list for "nuclear" related stuff, he found the recipe for a nuke. He immediately starts trying to assemble it... While lying through his teeth to the others who started asking what all this stuff he's asking for is about. The issue here is that whoever was handling the video editing noticed that Smiffy found the nuke schematic, and zoomed on his screen while playing foreboding music.
In episode #41 of Skyblock with Sips, Ross was using the new mob grinder for items and XP, and accidentally killed Trott as he walked past. Sips began to ridicule Ross for his traitorous and reckless actions, only to accidentally kill Alsmiffy with an arrow immediately afterwards.
Worms Clan Wars: The Dark Knight: Trott making fun of Nolan!Batman's voice becomes especially hilarious at the end, starting with this particular line: "Commissioner Gordon, I shit myself!"
Any time that they play Garry's Mod with Sips and/or the rest of the Yogscast.
Ross: (when he's about to kill someone, shouting manically) EAT SHIT! EAT SHIT! YOU'RE HUNGRY! EAT SHIT!
The Hat Corp series delivers a good one when the Sirs put Ross, who is a bit of a klutz when it comes to heights and lava, on the job of putting their company's huge sign up high in the air and filling a drum full of lava with a bucket. Ross keeps falling off of the sign while hilariously screaming, and his efforts to put a bit of lava in the drum see him set on fire numerous times. The crowning moment of death by fire is Episode 13, where after messing up and putting the lava on the drum instead of in it cause him to die. Upon respawning, he begins to shake angrily and shouts a couple of choice curse words.
HatCorp, episode 28. Ross, in an attempt to make paper from trees, ends up making every kind of sawmill available in the Yogscast Complete Pack.