How many comics does it take to screw in a light bulb?

Twelve.  One to screw it in, the other eleven to stand around and say, "That's not his light bulb."

What's the difference between a booker and a hooker?

There are some things a hooker won't do for money.

(OLD LADY TO COMIC) "I just wanted to tell you I thought you did very funny"

("Thank you") "I don't care what everyone else was saying.  I thought you did funny. So what do you do for a living?" ("I do stand-up comedy for a living")

"Oh...you mean they actually pay you."

What do they call the guy hanging around the club asking for money to find a place to sleep?

The MC.