I've haven't gone to the gym since high school but I find that the same is true for people working out at the park. Fats are usually lumbering around looking surly. Move slower than molasses and give you dirty looks when you run past them. Fit people on the other hand will usually be very amicable. As long as they aren't in the middle of an exercise they will usually strike up casual conversation and ask about your routine. I've had many an interesting conversation at the parallel bars and pull up bars.