It's funny how many hetero guys are so damned worried about "looking gay".
But I've been to San Francisco, and didn't see any gay guys walking around in lycra bike shorts!
And football and baseball players routinely wear tight pants. So, what's with all the "gay" fear?
Frankly, I think it's really more about fat guys being ashamed of their bodies...that's why most men these days wear the male equivalent of moo-moos (those baggy dresses from the '60's). Baggy pants, and baggy shirts worn outside of the pants are pretty good at hiding all those big guts and big butts.
+1
2 additional factors:
Those uncomfortable in their own skins tend to hate others that are comfortable.
Our puritan heritage is remarkably adept at making one miserable with his\her own body.