I got home today, opened the fridge, and discovered this:
Yes, it’s a bowl of completely dry cereal, staying nicely chilled. When I called M after school, I gave him and his friend permission to make a microwave pizza. So it’s unclear why they also felt a need to fill up a bowl with dry cereal and then leave it in the fridge, and they’re not home now for me to ask.
Maybe they felt cereal, like revenge, is a dish best served cold.