"Now that Baby Bowser sees us, he is going to want to ride us because he is a baby and he wants to ride donkeys and horsies.
Forgetting that blue Pikmin can't go through fire, SlimKirby confidently leads them through pillars of fire.
One time Slim (As Mario) was facing Luigi in a Mario Party 3 battle board. Luigi hits him once on an attack with double enhanced goombas for three damage, only for him to hit a reverse and finish off Slim in one turn from full health.
Several, a lot of them compiled in his 3 year anniversary videos.
"I LOST BY ONE COIN!"
"Hello everyone, Smithy here. Last time, Mario and his puny ant friends entered my factory, so I hit them with a giant hammer!"
Any of his Fuzzy-induced rambles in his SMW2 LP, particularly the one in Level 4-1.
Also, SlimKirby sings. Whether it's his song for Drake, Mario Party 5 boards, or even Princess Peach, he can sing.
Things get tense during Balance Boat, so he starts saying "eep" over and over, in his usual deadpan voice.
Episode 2 of his Super Mario RPG replay, Slim starts spending time with the toad citizens in the Mushroom Kingdom and saying funny things to them.
Slim plays the original Kirby's Dream Land, which is a game that can be beaten in less than half an hour. Over the credits he starts reflecting on the project in Sarcasm Mode.
Anything to do with Madame Wario's cat, Gooba (or known in the livestream, Goobatron).
It was also joked that Gooba is a drug crimelord. It doesn't help that some police cars passed Madame Wario's house.
One of Slim's friends constant attempts to get Slim to turn off the game during the final boss.
Slim plays the hard version of Kirby's Dream Land and it annoys him. The funniest of these funny moments is when he's tired of Gordos everywhere and does a sarcastic pitch for a Kirby ROM Hack where it's pretty much the same game, but with Gordos everywhere.
Video Game Logic
His What an Idiot moment (lampshaded) when he jumps right into Whispy Wood's attack and dies from it.
Olimar runs around in circles in Cavernous Abyss, then Slim decides to make up a song about it.
Blaine uses a Super Potion on his Rapidash... while it has full health. Pokemon Trainer Rob comments that Blaine should retire from being a gym leader for doing something that stupid.
In Pokemon Blue Kazio, SK decides to catch a Geodude for later use, and goes to check out its moveset. It only knows Self-Destruct.
... I have no words.
During The Simpsons: Hit & Run LP, he hosts a vote for what costume the character will wear for the entirety of the level (if a costume isn't required for certain missions). The reveal for Level 1 (Homer) was... Casual (read: under)wear, cue him calling out his audience for the fact it was 75% of the votes