Don't sweat it. Those guys are so into their own workout that they are paying no attention to you. If you see one of those big guys looking at you chances are they have noticed your dedication and are watching your form, not judging your size or strength. Take pride in it and give the dude a nod "hello" and keep going with your workout. That will get you respect and being a respected little dude carries alot of weight in itself.
As for me, I had a lot of time away from working out and am just starting back so I'm one of the little dudes again. It doesn't bother me because I know where I'll be by summer. Or maybe I'm just too old to give a fat babies ass what they think.