Kirby Super Star (and also Kirby Super Star Ultra): For Mike Kirby, he yells three times to cause damage to enemies. The first time, it's a screech. The second time, it's a megahorn. The third time, he sprouts a mohawk and screams into a mike, "DISMAL!!!"
When you start Milky Way Wishes, the tutorial tells you that you can't copy your enemies' abilities as you previously did. Cue Kirby's obvious, hilarious Oh Crap.
Kirby Super Star is a gold mine of these moments, really. But one that's particularly bound to make you crack up laughing is this kind of boss. The Computer Virus Battle is an Affectionate Parody of turn-based battles seen in JRPG, to the point the Italian version of Ultra calls it "Turn Battle". And when you win...
While Kirby Super Star (and Ultra) had the best quality and quantity of funny moments, other Kirby games have had some hilarious ones, too. Example, the ending of Kirby 64. Just... the ending. note Ribbon steals a kiss from Kirby, giving him a Crush Blush to the extent that he loses his balance and falls down the stars.
In Kirby 64, if you mix Fire with Spark, the resulting power involves Kirby rubbing a shiny plate thing on top of his head, and proceeds to light himself on fire, running around frantically with a hilarious expression.
Admit it, the first time you saw Meta Knight'sDramatic Unmask when you defeated him was hilarious. He looks just like Kirby, except dark blue, and immediately flees as if he's embarrassed.
All of the cutscenes in that game are hilarious, if only because of the Lemony Narrator.
Revenge of the King itself is one when you realize that Dedede is basically ripping off Meta Knight's scenario. When you get to Dedede's castle, which has the same background music as the later stages of the Halberd, you start seeing him conversing with his subjects about Kirby's progress just as Meta Knight did with his crew in Revenge of Meta Knight, then you get to the boss room and Dedede has donned a metal mask of his own and left a hammer in the middle of the arena for Kirby to use just like Meta Knight always tosses Kirby a sword before they duel, and the mask even splits in half inexplicably when you defeat him.