noun, masculine/a.ʁo.zœ.ʁ‿a.ʁo.ze/plural: arroseurs arrosés
the biter bit; one who receives the same comeuppance they planned for others, particularly through their own actions to bring this about, or such a situation
“C'est l'arroseur arrosé.” — He's been hoist(ed) by his own petard.
Literally, “waterer watered”; due to an eponymous 1895 short film.