Really hard to pick, since pretty much every other line is guaranteed to make you pee yourself.
One contender is the scene where Harry, Perry and Harmony convene at a revolting Hollywood Christmas party; Harmony's working there, Harry's high on demerol after surgery, and Perry is late, leading to this exchange:
Harry: What is it out here with these women? Harmony: Oh please, Harry, they're no different from anywhere else. Harry: Yes, they are. These are damaged goods, every one of them, from way back. I'm telling you, you take a guy who sleeps with 100 women a year, go into his childhood - dollars to doughnuts, it's relatively unspectacular. Now, you take one of these... gals, who sleeps with 100 guys a year, and I bet you if you look in their childhood, there's something rotten in Denver. Harmony: Denmark. Harry: That too! But it's abandonment, it's abuse, it's, "My uncle put his ping-ping in my papa!"... and then they all come out here! I mean, it's literally like someone took America by the East Coast and shook it, and all the normal girls managed to hang on. Harmony: OK, everyone who hates Harry raise your hand! [All the women in the club raise their hands] Perry [entering]: See that? Obedient little bitches too. [A girl offscreen shouts "Fuck you!" and hurls her drink at his head; he ducks smoothly and keeps walking.]
Harry being interrogated by two hitmen who can't agree on their names.
Mr. Frying Pan: Well now, here we all are. Ike, Mike and Mustard.
Harry: What the hell does that mean?
Mr Mustard: You know, I'm with him on this one man, that's pretty fuckin' obscure.
Mr Frying Pan: Horseshit, I hear that all the time.
Mr Mustard: You do?
Mr Frying Pan: Yeah, sure.
Mr Mustard: Where, at the 1942 club?
Mr Frying Pan: Hey, just cause you didn't get in...
Mr Mustard: Motherfucker I could've gotten in- (notices Harry making a break for it) HEY! Slow your roll, man!
Harry: This is bullshit! What are you gonna do, take me out here? There's security OW!
Mr Mustard: Keep talking. Keep talking.
Mr Frying Pan: You wanna know who we are? I'm the frying pan, see? And my boy over here, he's-
Harry calls Perry when he finds the body of the dead girl in his shower:
Harry: I peed on the corpse. Can they do, like, an ID from that? Perry: I'm sorry, you peed on...? Harry: On the corpse. My question is... Perry: No, my question. I get to go first. Why in pluperfect hell would you pee on the corpse?
Harmony gives Harry a lesson in basic grammar...
Harry: Umm, clearly I'm interrupting. I feel badly. Let me... What are you drinking? Harmony: Bad. Harry: Bad? Sorry... feel...? Harmony: You feel bad. Harry: Bad? Harmony: Badly is an adverb. So to say you feel badly would be saying that the mechanism which allows you to feel is broken.
(Shortly followed by...)
Perry: Go. Sleep badly. Any questions, hesitate to call. Harry: Bad. Perry: Excuse me? Harry: Sleep bad. Otherwise it makes it seem like the mechanism that allows you to sleep... Perry: What, fuckhead? Who taught you grammar? Badly's an adverb. Get out. Vanish.
The scene where Harry tries to interrogate a guy with Russian Roulette and immediately shoots him.
Harry: Well yeah, there was like an 8% chance.
Perry: Eight? Who taught you math?
In that same scene, Perry yells at Harry: "You, stop multiplying!"
When Gay Perry shoots the mook with a gun in his crotch.
Harry: Wow! I was glad you had a gun in there. For a second, I actually thought you could do that, like it was some big gay thing.
When Harry is listening to Harmony's story and pretending to take diligent notes...but really he's just doodling a cat, captioned with "ĄGato!".
Harry: I got 5 bucks says you could still get him.
Perry: Really? That's funny, I got a 10 that says "pass the pepper", I got two quarters singing harmony on Moonlight in Vermont.
Perry: Talking money.
Harry: A talking monkey?
Perry: A talking monkey, yeah. Came here from the future. Ugly sucker. Only says "Ficus".
The outtakes in their entirety. If you thought the movie was funny, just watch these guys when they screw up.
When Perry pretends there's a clue on the suitcase at the lake, tricks Harry into coming closer, and then bashes him on the head with it as punishment for tossing his pistol in the lake. He did it so smoothly that it's hysterical.
Major Mood Whiplash moment, but when Perry tells Harry the truth about his "acting career" and offers to let Harry punch him, Harry actually does. You can tell by the look on Perry's face that he didn't see it coming.
Perry: Thanks for coming, please stay for the end credits, if you're wondering who the best boy is, it's somebody's nephew, um, don't forget to validate your parking, and to all you good people in the Midwest, sorry we said fuck so much.