There are so many it's hard to narrow it down! I'm dating myself with some of my choices - since this is fantasy, I'm imagining them at their youthful physical peak (though in many cases I would still do them as they are now).
In no particular order -
--Mark-Paul Gosselaar: as the cocky college guy he played on Saved By The Bell: The College Years. Imagined taking him on his dorm bed or that I was a Professor blackmailing him in my office for a good grade
--Robert Pattinson: having my way with him at a back room of a Hollywood party, or he's Edward Cullen and I can cancel out his vampire powers, turn him back into a mortal and safely assault him.
--Tom Welling: similar to above - he's young Superman, but I have Kryptonite and can have my way with him.
--Jason Behr: I've always had a thing for this brooding Roswell hunk. He's doing shirtless pull-ups in his bedroom home alone when I do a home invasion and go to town on him. Anal assault, plus those big ears of his would make useful handles when I face-fuck him.
--Tom Cruise: the way he was in back in the eighties, Risky Business (sensitive preppy) and Top Gun (cocky jock) especially.
--Nick Jonas in his baseball uniform and stirrup pants, taken in the locker room.
--Chad Michael Murray: blond douchebag who needs to learn his place - punished for seducing yet another innocent girl.
--Rob Lowe: the ultimate prettyboy. Raped as punishment for that sex video.
--Ryan Reynolds: gangbanged in an abandoned warehouse
--Jared Padalecki: attacked by big tough truckers, strong enough to take this big guy down!