What gimmicks/characters were so bad that they destroyed a wrestler's career? I'd have to give it to the poor guy they gave the Muhammad Hassan character in the WWE from 2004-2005. Did he ever end up working anywhere in the business after that?
No, he actually left the business completely after that. Can't blame him.
Tiger Ali Singh was another one where his experience with the gimmick was so bad that he essentially quit wrestling completely, although a lot of that was due to locker room abuse.
The Spirit Squad basically killed off everyone not named Dolph Ziggler.