I saw Chris Rock randomly at the Comedy Store earlier this year, he showed up unannounced and asked if he could work on his material. He was up there for about 50 minutes and the amount of times he said "nope can't do that one, y'all would have my head on a spike if I said anything "bad" about them" ... etc. etc.
It was really interesting watching him do more of a practice run than the polished set because you could get an idea of their thoughts on a joke, whether it hit or missed, what is hot button. And how you can tell it has changed since he made it big in stand up.
He did a joke about abortion that I was dying at, but half the room was cringing, and after wards he addressed the audience and said, see, "these people understand a joke" the rest of yall thinking you're too good, even if you smiled, you thought that was funny. Just stop it." and that got a good laugh.