What does “sich rächen” mean in German?

Sich rächen means to get even — a reflexive verb built around die Rache (“revenge”). The reflexive sich matters: you don’t just “rächen” someone, you “sich an jemandem rächen” (get revenge on them), putting the person you’re avenging yourself against into a separate an-phrase. It’s a genuinely useful pattern for describing paybacks of any size, petty or serious.

The clip’s payback is delightfully petty: a girl ties her crush’s shoelace to the drawstring of his hoodie after he steals her last chicken nugget, then calls the teacher over to watch him try to stand up. That’s sich an jemandem rächen in miniature — proportionate, public, and immensely satisfying to the person doing it.