My MIL saves 1 green bean. She saves 1/4 of a hard boiled egg. One slice of tomato. Every time she cuts bread, she scrapes up the crumbs into a bowl that she uses later for bread crumbs. However, you have to realize she was raised in a much more extreme time. First, she is a farmers wife, and knows the value of food from hard work and does not waste - ever. Second, she grew up during the war, where every single thing was scarce - even if you did have a farm. Being in europe in the war was different than being in the states; I mean it wasn't just coffee and sugar rations.
This. A dip mom or mil made and at at home and then brought, not my favorite but OK. A dip she made and then shared with her bridge club and then brought, um, no, gross. Not logical, but I guess it is like germs. I don't mind licking off my child's face if there isn't a napkin nearby, but I wouldn't do it to anther kid.
Was it her appetizer? I would be fine with MIL bringing over an appetizer she made or an opened box of somethign she had. If it was leftovers from somebody else that she saved and brought to my house, then I would think that was weird. It doesn't make a lot of sense logically, but that's what I would be comfortable with.