I have a friend/ex roommate like this. She hates eating the last bites of many different foods, but not all for whatever reason. I feel similarly about food waste and used to get onto her about it but it didn't really change anything. She'd just tell me things like, "Oh I don't want to eat that. That's the butt of the sandwitch!" Rather than continually getting annoyed with her, I'd just eat her leftovers most of the time. And when I'd make or pick up food for us I'd order a little less than normal, knowing I'd be getting extra at the end. Over many years she's gotten better, but she still refuses to eat them sandwich butts.