It's getting a shocked laugh out of the audience by saying things he "shouldn't" say and then excusing it by saying it's a character or (as is often in Jimmy Carr's case) trying to deconstruct it as a meta commentary on what is acceptable in humour. Carr, at least, is a skilled joke technician and very knowledgeable about comedy (my Dad wasn't his biggest fan but thought his book was excellent and used it as a reference in his MA on the linguistics of humour) but it's still a fig leaf being deployed to tell the same punching down jokes that were being told in working men's clubs and the New Wave of British Comedy swept aside.

Taste is subjective but I'm not a fan - it's an excuse for pretty lazy comedy. Frankie Boyle was much funnier (IMHO) when punching up than he was when he was making jokes about Jordan's son.