Essentially it goes like this:
Someone who is "overly masculine" to the point of bodybuilding, etc., is obviously obsessed with masculinity. They are obsessed with masculinity because they don't value femininity at all -- because they're gay. ESPECIALLY if they are constantly around men who have a similar physique. In Japan nothing is gayer than a bodybuilder's gym.
If you really want to get the girls, you have a boyish charm, and focus on a softer form of male beauty.
Also, if you like to wear pink frilly dresses it's under the assumption that you're a perv, not gay. (Think of Ed Wood and why he crossdressed. He did it because he WAS into women, and styling himself as one made him feel closer to them.)
That said, there is also an effeminate gay stereotype in Japan, but they are treated almost as women rather than gay men. ...but what's gayer -- an obsession with dresses or an obsession with ripped beefy muscles and oiled glistening skin?
(See other reply to this post for an explanation of "Bara")