It may seem that the Yaoi Loving world is predominantly female, but looks are almost always deceiving. This is one of those times. Yes, girls go around proclaiming their love for ManonManime (c) more often than boys, but that doesn't mean that the boys aren't into it. It took my fangirl-ish-ness to get a guy in my school's anime club to admit that, not only was he bi, but he was all into yaoi. I have a straight male friend who likes looking at yaoi with me because he considers it sexy and very romantic. He's a sap and so am I.
All in all, yaoi is 50/50 in the female to male ratio. It's just harder for a male (especially a straight one) to admit to liking something that is homosexual.