That's a tough one as there are a lot of sarcastic comics out there. I'd say the least offensive but still funny comic I can think of who uses a lot of sarcasim is Bill Engval. He's the comic who is famous for his "Here's your sign" jokes which are pure sarcasim. One of my favorites is the one where he says something like "I got in an elevator the other day. We were on the ground floor and I pressed the button for the third floor. Another guy got in with me, looked at the lit button for level 3, pressed it again himself and said 'Going up?' I looked at him for a minute and said 'Nope, just going to stand in the elevator and ride it up and and down all day. It's my favorite ride. Here's your sign!'" The "sign" being an imaginary one that he says he'd like to have people who make stupid remarks wear that says "I'm stupid". "That way, we'd all have a warning that we're being approached by a stupid person. So we're fore-warned and not so surprised when they say or do something really stupid".