Jackie Mason
Jackie Mason never lived down a 1964 Ed Sullivan Show appearance. He'd earned a recurring slot, but it was revoked when he intentionally gave the finger to both live and studio audiences. Sullivan didn't tolerate that kind of stuff, and Mason's career suffered because of it.
Michael Vick
Former football player Michael Vick was charged with organizing dog fighting rings in 2006. He went to prison, came back, and had a somewhat successful career after, but many people feel that animal abuse doesn't deserve forgiveness. Hopefully, he's never allowed to own pets.