I see a lot of jokes online about how pineapple on pizza is gross, but it's not really that bad.  I can enjoy a Hawaiian pizza once in a while.  The obvious gross pizza topping is anchovies.  I delivered pizzas for a while and anytime there was an anchovy pizza in the order you could totally smell it overpowering everything else in the car.  I ventured to taste them a couple times and they're mostly just salty, but they're overpowering in flavor as well as smell.  You almost may as well not get any other toppings because all you're going to taste are the anchovies.  

On a side note I can't help but imagine an 80's hair rock fanatic who also happens to be a cannibal who orders Bon Jovis on his pizza.  Ouch.  I think I gave jokes a bad name with that one.  I must have been livin' on a prayer when I came up with it, but I wanted to go out in a blaze of glory.  I'll show myself out now.