Now, I know a fair share of homosexuals, and they're not flamboyant at all. In fact, most are more introverted than anything.
That they're flamboyant is generally a more obvious sign that they're metrosexual. At least, the original metrosexual. The new metrosexual as "the guy who cares more about his appearance than anything else" is just a douchebag, but the original metrosexual is a guy who pretends to be gay so all the girls will go "oooh I wish he was straight" and go out with him when they find out he actually is.
It's sort of like growing beards. "I bet that guy would be so handsome without that beard" and then when they shave it off they're all like "Oh Em Gee Want Want Want" when without the beard they wouldn't have obsessed over him in the first place.