Heh. Harley Quinn is a good one, I always liked it when the NPCs in Arkham City commented on the danger of Harley prancing around in that tight little outfit while locked up in a city full of violent criminals. I always thought "Damn straight! She'd be raped in like 5 seconds flat if the Joker wasn't around to protect her." If only someone made a mod for the game like that...
Another costume fantasy of mine is Dorothy Gale from The Wizard of Oz. I'm amazed that searches turn up pretty much nothing for rape fantasies involving that character.