I’ve seen a few people put their delivered pizza in the oven after everyone grabs a piece to keep it warm. I’ve also seen a lot of those people forget the pizza is in there and either have to throw it out or only noticed after they preheated their oven.
As long as the temperature is below 451F/233C, there should be no danger of fire.
Pro Tip: Keep masking tape in the kitchen. If you do something weird like storing a pizza in the oven, put a piece of masking tape over the oven dial as a reminder. Masking tape is good for putting a date on things going into the fridge too.