I really should have read all the answers and voted the last one instead of the first.
I fantasise all the time, I've thought about any number of people and unrelated things during sex and masturbation. I don't see me as being a bad guy for it, rather absent minded and easily distracted, yes. Masturbating, I rarely think of only one woman so it'd be a lie not to vote for that. During sex I think I've always done it, except for the first few times with someone.