I have never for the life of me understood putting mayonnaise on a burger. I hadn't even heard of such a thing until we got stationed in California, and apparently that's the default there (as I found out the first time I ordered a burger in a restaurant and nearly choked on the unexpected awfulness; they didn't bother mentioning it on the menu, or I'd have known to order mine without). I like mayonnaise, but never on beef! In my mind, it's like ketchup and ice cream - two great tastes that should never be consumed at the same time. (I understand there are others who think otherwise, but it's just not for me.)
Johnathan