There's nothing wrong with walking away hun. Or if they sit at the table, just pick yourself up and walk off without saying a word. That says everything right there. You don't have to sit there and put up with it. You see them walking in a group just turn away go else where. They are not welcomed in your world, so easiest thing to do is to turn away. To do anything more than that like yell or fight puts them right back in your world actively like and trigger the bipolar worse. Your friends will understand why you got up and walked off eventually. Nobody will hold that against you. Good luck Hun and please hold your lunch!