Dude, as genetic as anything is in life, everything comes down to choice.  As pain is defined, it is the largest aphrodisiac in the world, and if one chooses to accept pain or decline it, it is still a mental concept and not a physical one.  It would be as such to say, if a man is fat (genetically), and doesn't like being called fat, or like anyone making 'way' for him when he walks by, he will make strides to lose weight.  Thus, he has tilted the pleasure-pain balance in the favor of how he wants to feel, same as a man who likes being fat.  If the latter wants to eat a bunch of food and not care about his health, it's something he chooses.  But to be fair, there are definite circumstances where a biological organism has no choice.  All I'm saying is that it's not so widespread to affect every single person in the world that claims genetic variation for any one type of characteristic.  As my best friend says (and yes, he's bi), everyone is both homosexual and heterosexual: we all just kind of lean one way more than the other based on how we feel about a person.

And to make you all laugh, yes, I still go to gay bars.  It's all about the free shots, and the statistic of 80% of straight women go there to get away from straight guys, and I just love to disappoint them.