Not for the guys. They think about it all of the time, Especially that one that you have been friends with so long that you have never thought of him in any sexual context because that would be like thinking about fucking your brother..... .Yeah, that one, he has thought about plowing you a hundred times.
Funny thing is that you will probably think I am joking. I have 2 girls that I have known since kindergarten and I am best of friends with both of them. One of them I want to make a move on so badly but neither her nor her boyfriend deserve that (he is an army guy, training out of the state). The other one I confessed my crush to this summer and we hooked up near the very end of summer and I have maybe seen her twice since, we'll see what winter break is like.
Anyways, unless he is a confirmed homosexual, your "platonic" male bff wants to do vulgar things to and with you. Don't believe me? Try dancing with him and see if he dances any differently than a guy trying to get with you, or better yet tell him "I know what you are thinking about" next time he spaces out when it is just the two of you together. If he wasn't thinking about sex before, he will be after you say that