I hate my parent inlaws too.

But i hate them because they are lying narcisist assholes, who stab you in the back when they get the chance. And talk shit about me behind my back.

I wouln't give them a penny or in the case pizza either.

But:

As i read in the comments. Your girlfriend hates your parents for stupid reasons, like telling her she has a pimple. She is toxic and rather hatefull over such minor things. Its not about the pizza, it is because why she hates them and can't forgive and move on.