/Begin Rant
This isn't about pizza, is it? Heck, it isn't even about food. This is about you getting to mock other people without feeling bad for it. "Look at these rubes, eating pineapple on their pizza," you say loudly, then quickly look around the room and hope that someone else will say "yeah! I agree!" and give you that sweet burst of validation you've been craving. The eye contact, that little chin pop of solidarity. Now you aren't a common bully, bothering people who are otherwise enjoying their day. You're a popular bully, with cronies that will sneer and say stuff like "huh huh huh yeah, good one Chad!" when you act out.
That's what this is all about, isn't it? Pineapple as a pizza topping was never the issue...just like calling a kid with glasses "four-eyes" is never about vision correction.
/End Rant
TL;DR: be kind to one another. Let people enjoy things. Remember that you are in public. Don't feed the trolls or validate the bullies, but don't let their behavior slide--report them without engagement, then click away.