When John pretends he's bought Lisa a fancy new sports car. And teases her about it.
Lisa: Oh, my God! John, you didn't!
John: No, I didn't. The van's around the corner. But don't tell me you don't care about money.
Lisa: That's not funny.
John: (starts imitating her) Oh John, you didn't! You didn't!
Lisa: (starts laughing under her breath) That's not funny.
The whole Dolittle/Rodney scene. Which eventually ends with Rodney's cage is strapped to the top of Dolittle's car, which happens to be cruising down the highway!
Rodney: ... Come on, Doc! I'm getting whisker-whipped up here! Hey - this is cruel to animals!
Dr. Dolittle: One more word, and I'm letting you out! I'll leave you in the wild! With the REAL animals! See how much talk you do when squirrels are kickin' your ass in!
Rodney: Fine, then I'll just sing! (he then proceeds to sing "Blowin' In the Wind," way off tune) ..."The answer, my friend, is blowin' in the wind..."
Dr. Dolittle: SHUT UP! (turns the radio way up)
Rodney: (still singing) ... This guinea pig is blowin' in the wind!
Dr. Dolittle: I can't hear you! I'm groovin'!
Rodney: ...Why do they call me "guinea pig," anyway? I ain't Italian, and I'm not pork...!
Dr. Dolittle: SHUT UP, I SAID!