You're out with friends and eat way too much junk food. You tell your best friend you're stuffed and you're worried you're going to get fat because you seem to do this all the time. Your best friend tells you that she can pig out as much as she wants without gaining weight. She just throws up after. She offers to show you how to make yourself throw up.

Say "Gross. I can't believe you'd do that!"

Try it just this once.

Tell your friend what will happen to her body if she continues.