Man, I really wish I could remember what side I got this anecdote from - apparently really early on in Roddick's career, a woman asked him for an autograph thinking that he was Sean William Scott. Upon learning he wasn't, the woman went on her way, but not before telling him interesting it was that he looked like someone famous!
Good thing he stuck with tennis, outside of commercials - where he was actually pretty serviceable - A-Rod was not a... convincing actor.