In the movie All That Jazz, Joe Gideon, the main character and director, was editing a movie called The Stand Up, and you saw quite a few clips of the guy doing his stand up routine. I didn’t find it all that funny, but there aren’t too many standups that I do laugh at.
It was short, but I remember Woody Allen in Annie Hall’s stand up scene being funny. I haven’t seen it in many years, though.
Man on the Moon with Jim Carrey as Andy Kaufman had some good stuff, especially near the beginning with Carrey as Kaufman as “Foreign Man” as Elvis.
Weird since sandler, rogan, ansari, and hill are ALL standups by training. also, i’m positive i’ve seen plaza on youtube doing standup where she does stand-up impersonating sarah silverman’s standup - rather well too.
I’m guessing that the OP isn’t interested in performances in which the actor is a stand-up comedian just doing his regular act in the context of a movie, such as Louis C.K. in his sitcom, or Woody Allen in Annie Hall. And it also can’t be recreations of a real standup act, such as Andy Kaufman’s act in Man on the Moon. It should be like a Studio 60 on Sunset Strip scenario, in which an actor is playing a fictional character (not essentially just himself or herself) doing an act written for the character in the movie.
Furthermore, in the movie, it has to be in the context of an actual portrayal of a standup act, so Jerry Lewis generally clowning wouldn’t count.
Robin Williams in Good Morning, Vietnam, might be a border case, but really Williams was (1) just doing his regular Robin Williams shtik in front of the camera and (2) he was portraying a real person who did actually try to be a funny performer, so I think it shouldn’t count.
Dave Chappelle in The Nutty Professor would count.
if it’s the latter, i nominate quentin tarantino’s “piddling on the bar” joke in “desperado.”
For the former, Abbott & Costello performing “Who’s on First” in The Naughty Nineties.
In front of a crowd, or just posting an impression on YouTube? There’s a big divide there.
She’d never performed live standup before Apatow made her for Funny People. I believe the same is true for one of the other smaller parts, and I believe Rogan said he hadn’t done standup since very, very early in his career and was never good at it.
Even worse: Data could pick any stand-up comedian in history, and he went and chose Joe Piscopo???:rolleyes:
There was an episode in WKRP in Cincinnati, where Venus Flytrap dreams he’s doing stand up. It started out pretty funny, but a heckler began to bother him and it all fell apart.
Vic Hitler in Hill Street Blues was very funny with his quips, though, of course, it didn’t work out when he went on stage (though he probably would have been fine if he had stayed awake).
OK, who did you think an android with no sense of humor would pick? 
Ventriloquist Nina Conti (and her main puppet, Monk) was (were) in the Christopher Guest movie For Your Consideration playing a ventriloquist “weather girl” who was funny.
So she wasn’t doing stand-up and wasn’t doing her routine but she was being a funny ventriloquist in a movie.