I like to piss them off by stating that after tons of work, I managed to get up from my weight of 100 pounds.  I'm 6'1" so that was not a good weight.  (Thyroid disorder, not an eating disorder.)  I love to bitch and moan about how hard it is to eat that much food just to watch them get madder by the second.  They can't even say anything to me about "fat shaming" because I'm referring to myself and an actual medical condition.  (As opposed to their medical condition.  Every time their elbow bends, their mouth pops open.)