I'm gay and get freaked out in the locker room because I'm worried the straight guys there will think I'm just like that guy was to you. There are those of us out there that are not, and I appreciate that you seem to recognize it was an individual situation. (Though admittedly there's a reason for stereotypes.)
I also don't like to get changed in the locker room and use it for the restroom, sink, and storage only with a few exeptions. I've always been self-conscious about my body in front of anyone when changing, I would assume because of my weight. I do think it's funny how many older people let it all hang out.
So in short, yes I get uncomfortable around it and I wish gyms had a little more privacy for everyone. Let me further clarify by saying even if I had a six pack I don't think I'd be comfortable around it.
Highest weight: 435 6/2009
Lowest weight: 278 4/2010
Weight when joining fitday: 324 11/7/11
Current weight: 323
Goal weight: 220lbs (then we'll see)