Go over and tell them that staring costs money, or the option is you can punchify their face for free!
I used to worry about what people thought of me at the gym (heck, i still do, and always did, even when I was eating disorder skinny) but one day, a friend of mine said "Heather, when you see someone who is big at the gym, what do you think about them?" And I realized that-If I thought anything at all, usually I'm too busy trying to keep from dying on the treadmill-Good for anyone trying to make a positive life change!
I dunno. Also, a lot of times, I really am too busy WORKING MY PECS, YAH, to notice other people.