This is totally me!
I too, am 100% gay, but am quite turned on by watching a straight guy eat some pussy! I think it the fact that the guy is really into it and really eats her out, that get me hard. It's one of the few parts of straight porn that seems passionate to me. And it's also something that you don't see in every straight porno. I also like it because, I suppose, it's a submissive role, especially if it's femdom.