Andrea, I think the examples in your original post are kind of contradictory. "
"Don't worry about going to the gym when you're fat, people are focusing on their own workouts" and "Don't worry about eating junk food when you're fat, nobody will notice anyway" are very different. From my experience and what I have heard others say, they're both kind of untrue but in very different ways.
When I see a fat person working out, I think, "Good for them, they're trying to make a change." My DH, who has never been obese, has the same feeling about overweight people at the gym. He says he often feels like he wants to go up to them and say "You're doing great" or something like that. I really don't think that people at the gym generally judge fat people for being fat in a negative way, because the fact that that person is IN THE GYM is evidence that they are trying to overcome their weight problem.
However, when I see a fat person eating junk food, I do admit that I have negative judgmental thoughts. I have these same thoughts about myself sometimes. However, I remind myself, when I was losing weight I allowed myself one cheat meal per week. How do I know that that person eating ice cream didn't spend the last week eating nothing but healthy food? (I admit I am more judgmental when observing the contents of people's carts at the supermarket.)
I think judging people is part of human nature. The important thing is to keep your judgments to yourself and not saying anything to the person you are judging. When I was a teenager, maybe 13 years old, my father started telling me that I was fat. Sure, his intent may have been to help me, but the fact is: I was not fat when I was that age. I wasn't skinny, but I certainly wasn't at an unhealthy weight. Being told that I was fat just made me feel like crap, which made me eat more to comfort myself, which made me get actually for real fat.
DH and I talk about this kind of thing because I feel that it's especially important since we're about to have kids, and our kids will be girls. IMO it is never appropriate, ever, to tell a girl or a teenager that she is fat. Nothing good will ever come of it. Similarly, making judgmental comments about other people's weight in front of kids makes them internalize "that is bad, if I am like that then I am a bad person." This applies to judging yourself too! DH has a tendency to say negative things about himself. For example, yesterday he accidentally didn't pull his car into the garage far enough, and when he shut the garage door it hit the bumper of his car and scratched it a little. He comes into the house and says, "I'm so stupid. Why am I always such an idiot?" The fact is that he's not stupid, he just did something dumb on this particular occasion. Smart people do dumb things. But him saying that out loud not only makes other people more inclined to believe that he's stupid, but it makes people question their own intelligence. I mean, for an example, if you hear a supermodel say "I'm so fat," then you think, "Wow, if she is fat, then I must be a real whale."
I guess what I'm trying to say is making judgments about other people and about yourself is normal, but saying them out loud is never a good idea.
(And for the record, I'd rather be fat again than lose an eye or lose my job.)