1. get self-confidence.
2. look them each individually in the eyes, straight in the eyes.
3. tell them not to do it anymore in a firm, confident tone. not in a whiny, little pansy voice that is so fashionable in high school. in the tone of voice your mother might use if she were to say, "Fat Kid, you will NOT leave the table until you eat ALL of your vegetables." or, "You will NOT borrow the car until you pay off your debt."