Sorry but some of these posts sound crazy to Americans...Butter on a peanut butter sandwich?? Butter AND mayo??? Butter on a tuna mayo sandwich, wtf
Mustard, mayo, cream cheese, pesto, hummus, BBQ sauce, these are all much tastier spreads in our eyes
I mean if you love butter crack on, but Americans are not 'wrong' we just have different sandwich traditions. In my home region we don't do British type sandwiches at all, more Italian/Jewish/German influenced.