The problem with that is opinions is something everyone has. They are for only them.
Your opinion can be that people who like pineapple on pizza are stupid, but that's rude.
A prejudice is something that you can't change about somebody else.
So your belief is that pineapple doesn't belong on pizza which is fine but it is not a prejudice
I am not opposed to pineapple on pizza, but if it's the only pizza available I will eat it. If you think pizza is either incomplete without pineapple, or ruined with it, I will respect your opinion.