What did the bulimic say at dinner before going to the restroom? "I'll be right back, going for seconds."
I don't really think this was very funny or fun.
It's a joke, you're just too sensitive. Get over it.
People who suffer from bulimia aren't meant to be a punchline to one of your jokes. These people suffer a lot, and if you continue to make fun of people who deal with such terrible things then you will not have many people to hang out with. Have you tried telling safer jokes?