Although I agree with others that pineapple on pizza is an abomination, it is very common here in California, and is often referred to as a Hawaiian Pizza. Unfortunately, pineapple is not the only highly inappropriate thing that Californians put on their pizza. Chicagoans seem to be of a similar mind; they often pile every imaginable piece of crap of their pizza, which ends up looking like a vegetable garden.
I am a straight cheese pizza guy from New York who grew up on consistently excellent pizza. Adding pepperoni, sausage, and mushrooms is about as far as I’ll go, if pressed, but people here think that’s plain, boring, and tasteless. Needless to say, in most cases they have never even tried it.