I'm gonna go with game genres, specifically roguelikes and rhythm-based games. They sound terrible together and yet, Crypt of the Necrodancer (and also Cadence of Hyrule) is the shit.

Peanut butter, mayo, dill pickle sandwich. Might not be too rare, I've met a few other people who eat variations of this but damn is it good.

You gotta watch out though cuz all that mayo will sneak up on you.

Peanut butter on a meat sandwich. Any sandwich. I like roast beef peanut butter combo.

Bacon milkshake. Got to make sure the bacon is cooked proper to get some nice crumbles and it adds an amazing salty savory that really makes the milkshake flavor pop. Doesn't work with all flavors

Well, here in Italy they complain a lot about pineapple on pizza but then eat ham on melon

Liquorice (or even better, salted liquorice) and coffee.

Sounds alien, I know. You just gotta trust the process though.

French fries and mayo

Froot Loops cereal with chocolate milk. Just trust me.