Also, the part when Ace makes shadow puppets during the slideshow. Especially when Cadby steps in front of the screen. "Heigh-ho Silver, away!"
If anybody else bent over, turned around and pantomimed talking out of their ass, most people would strain themselves rolling their eyes. When Jim Carrey does it, spouting out horrible puns all the way? Awesome!
Ace's Butt: "WHATSA MATTER? AFRAID I'LL MAKE A STINK?"
In the second movie, a failed attempt to sneak into the bad guys' hideout leaves Ace knocked out, and him and his pet monkey strapped to a raft heading downstream. Ace bites through the monkey's ropes first, then tells it to undo his. The monkey starts, but then takes a look at the Inevitable Waterfall and decides to get the hell out of dodge instead. Ace's reaction as he goes over the edge is hilarious.
Ace and Melissa on their way into a very ritzy party:
Melissa: I'm really going out on a limb here, Ventura. Camp's social events are strictly A-list.
Melissa: I swear, if you do anything to embarrass me in front of Camp-
Ace: What? Like this? (makes faces)
Randomly during the party, Ace reaches over and screws up a cello player's performance for no reason other than pure whimsy. (Jim Carreyimprovised that.)
Ace's reaction to finding out that Lois Einhorn is actually Ray Finkle. It starts when he's wangsting over his inability to crack the case, when he notices his dog's fur draped over a photo of Ray Finkle like hair. It comes with its own built-in spoiler: Right when the realization begins, the film starts playing the song "The Crying Game", which the scene is an obvious spoof of.
When Ace is pretending to be a mental patient football player to sneak into a institution, he tackles the doctor in super slow motion, then reverses it for instant replay, including all of his dialogue.
Ace punching out the Monopoly Guy lookalike and parading him around like a stole, then shaking his mouth around like a puppet.
Ace: Do not pass go! Do not collect two-hundred dollars!
"That's what you stepped in, that's what was on your shoe, and that explains the abrasion on your palm! Let me run that back for ya. Mlap ruoy no noisarba eht snialpxe taht dna eohs ruoy no saw tahw s'taht ni deppets uoy tahw s'tah... That's what you stepped in, that's what was on your shoe, and THAT EXPLAINS THE ABRASION! ON! YOUR! PALM! DAMN I'M GOOD! (pelvic thrusts) Can you feel it?!"
To reiterate, Ace taking over for the frontman at the metal concert and just growling noiselessly while gesturing like he's talking to the crowd... and the band just goes right with it.
After rescuing the kidnapped dog, Ace tells him, "the (car) engine's flooded. No problem, we'll just wait a few minutes". As the goon begins smashing his car window, without missing a beat, Ace declares, "Or we could try it now!"