I had a friend in school that we all refused to eat out with. She'd dunk fries in the milkshake, eat the burger by taking it apart and eating it layer by layer (like, eat the bun, then the pickles, then the cheese, then the burger, then the bottom bun); and I once witnessed her finish her drink, finish her meal, and then take her drink straw and suck up the remaining mayo she was using for dipping.
Fucking serial killer, I swear to god there was something broken in that girls think-meat. Other than her insane, hooker strangling eating habits she was pretty nice though.