Obviously US pizza eaters are very weird people. Their least favorite toppings are pineapple, anchovies and mushrooms. Not liking mushrooms on pizza is just wrong.
It's impossible cook a fresh mushroom dry on top of a pizza, so they make the cheese watery. Precooked like carmelized onions are good but few places do that
I never really got why pineapple on pizza is considered weird - at least here in the UK it's common to get a gammon steak with pineapple on it, or have roast pork with apple sauce which is a similar concept. I can get not liking it if it isn't your thing, but I don't think it is a particularly odd topping.
On the gammon with pineapple thing - I remember a popular science programme when I was young (Tomorrow's World maybe) about gammon and pineapple. It started with a story from the Second World War about some soldiers in the Pacific theatre, who were stranded in occupied territory, and survived by coming out at night and stealing pineapples from the fields. Apparently all their teeth fell out, and this was not because the sugar in the pineapples had simply rotted their teeth as the soldiers initially thought, but because of enzymes in the pineapples softening their gums. And it is these enzymes that soften meat and make pineapple a great meat tenderiser, and hence a great accompaniment for gammon.
