I have a feeling this caption is fairly self-explanatory.
Rather than talk about this caption, I think I'm just going to quote Joe Sixpack (and if you haven't check out that site by now I highly recommend you do).
"So you get a little turned on when you think about switching genders? So what!? Everybody's got some sort of freakishly bizarre thrill they never talk about. That's no reason to get all weirded out over this stuff.