In the young hipster community MFM threesomes are now really popular becuase hipster girls think it's cool to watch two "straight" guys blow each other, and the dudes are willing to do it as long as it gets them pussy.
And pegging has become super popular as well.
I think that a lot of these straight guys who have sex wtih other guys are doing it to impress girls - which would, to my mind, make them not gay.