So I think this works better for some people than others, and better in certain situations than other (pubescent boys are perhaps the most likely group).
@Mr.ShinyandNew安宇 I...don't know, both would be huge turn-offs if it were a friend.
I think perhaps the best criterion we have so far come up with is this:
If you are aroused by imagining female bodies, you are to some degree straight (so straight or bi).
The only complicating factor is that imagining sex, of any kind, can also be arousing.