My husband's family butter EVERY kind of sandwich. Peanut butter, Vegemite (blergh), jam, marmalade, salad...yes I said salad, cheese, baked bean, you name it & they'll butter it. I even saw one of them put butter on an avocado sandwich! Oh, and they put butter on certain types of cake.
I don't get it...I guess my Mum didn't like butter much so I think it's odd to butter everything.