Only acceptable usage of American Cheese IMO is grilled cheese, ham sandwich, and occasionally on a burger.
In regards to Mayo and fries, first of all nothing should be ON the fries, fries are meant to be dipped. Mix some Mayo and Sriracha, dip your fries in that and shut your mouth, because ya'll are wrong. It's tremendous.
A Pepperoni and sausage pizza dipped in some house ranch ain't bad at all. I'd be more inclined to do it if it didn't make me feel like a fat fuck, so I refrain. As far as taste tho, it definitely works.