The Chernabog Impression when the Thief tries to steal the giant ruby.
Right at the beginning of the movie, the thief tries to steal some bananas from an old lady who reaches her GIANT MAN HANDS through her tunic and beats the ever-loving crap out of him. Even better during the initial encounter with the Brigands... whom she beats the everloving SHIT out of one by one.
"OPEN FOR THE ROYAL POLO PONIES!" The singers in the background just make that small moment hilarious.
After his long struggle up the pipes, the Thief pulls on a cord that turns out to flush them, giving a Pink Panther-esque glance at the camera as he's pulled all the way back down.
The Thief getting whacked around during the polo game. Every time.
The Thief picking his own pocket.
A way to redeem the Miramax version of the film is to pretend the bulk of the Thief's monologue isn't actually telling the story but mocking it. It makes it a lot more amusing.
Some of the Thief's snark in the Miramax version is pretty funny:
When he sneaks into the cobbler's shop in the beginning and when he sees all the mess: "What a dump! Nobody lives like this except college kids!"
When he falls into the moat: "I can't help but question the color of this water. I'm gonna stink for days. And I just had this robe dry-cleaned!"
When he sneaks into the Princess's bathroom: "Hey, look! Ha-ha! Soap! So that's what it looks like! I've heard of it in storybooks and songs!"
And then immediately afterwards, when he spots Princess YumYum in her bath: "What's that? ...Oh, a naked lady." Said in a really disappointed tone.
When he's chased through the palace by Tack, he notes the extremely stylized checkered backgrounds: "Man, who decorated this place?"
As he steals the three golden balls: "You're gonna buy me a castle by the sea! And you're gonna buy me everything I need to turn the basement into a rec room! And with you — I tell you, sweetheart — I'm going to Disneyland!"
While climbing up the mountain made out of stone hands: "I'd be dead if this mountain started to applaud!"
Chasing one of the golden balls: "If I find out that's just gold paint...!"
And when he steals the "THE END" letters: "I'll just hold onto these little goodies until the reviews come out!"
When he keeps smacking into warning signs: "They should have a sign: 'Beware of Signs.'"
Yum Yum smelling the Thief in the bathroom, helped by the actress's unusually snarky delivery. "Maybe the pipes are backed up. Maybe something died."