It depends. There was the Pryor/Wilder movie See No Evil, Hear No Evil. There is the scene in What Ever Happened To Baby Janewhere Joan Crawford's character said "You wouldn't do this if I wasn't in this wheelchair!". Betty Davis' character said "But you ARE in that wheelchair!". I think because of the delivery of the lines I thought it was funny. But if you are laughing at them instead of with them, then it is not acceptable.
When you think about it, saying things like "Duhhhh" or "That's retarded" falls under this, but I don't think people aren't as sensitive about them. Making fun of a specific person about their disability - definite no.