Pretty much any scene with Peter Vincent falls under this but especially this exchange between Peter and his female assistant, Ginger.
Peter: Fuck you!
Ginger: I will fuck me, who else is gonna do it?
Not to mention the time when Peter tells Ginger she was late for her entrance in one of the acts. She responds that he was early... in bed.
Also, when Peter tells Ginger to get the door.
Ginger: I'm watching my show, you get it!
Peter: You're 'tivoing' it, you lazy cow!
Peter: I guess I don't wanna be a man like me, either. *Opens his coat to reveal an impressive arsenal of weaponry.* Let's kill something.
Actually seeing the Doctor use profanity is in and of itself hilarious.
A subtle one: while Charley is lurking through Jerry's house to escape with Doris, Jerry is seen watching one of Real Housewives TV series and laughing.
When Peter's gun jams:
Peter:*click* Fucking eBay!
"I'm gonna pop your cherry."
Ed's not really the best vampire.
To put this in perspective: he loses an arm when he fails to get to Peter Vincent before he enters his panic room, gets chomped in the neck by an axe, has a bookcase dropped on him, gets hit with a mace and then finally get staked.
On the other hand, considering he just got turned and he endured all THAT before he got staked, maybe he's actually a really GOOD vampire in the very short time frame he had as one.
Charley's mom staking Jerry with the Century 21 sign and his reaction to it
Then Charley using another car to slam into his mother's van and knock it over onto Jerry
"That's a mighty big cross you got there. . ."
Jerry's mock horror in that scene really sells it.
Mark, David Franco's character. His role was basically playing his Scrubs role but Up to Eleven as a high school bully, and when he becomes a vampire, he drops the funny. However, his line after being cured from his curse is this:
Mark: Man, that was some fucked up night.
The final scene of the film where Charley and Amy are about to have sex in Peter's penthouse, and Peter accidentally interrupts them to come back for his phone. Before he leaves he tells Charley "not to do anything he wouldn't do", but admits that doesn't narrow it down much.