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What does “wydurniać się” mean in Polish?

In this clip, a birthday girl snaps at her mom, “kończ się wydurniać” — “stop fooling around.” Wydurniać się is built straight on durny, Polish’s everyday colloquial word for “foolish” or “not thinking straight.” Add the reflexive się and durny turns into a verb for clowning around — play-acting silly rather than actually being dumb.

Durny traces back to a Proto-Slavic root, *dur-, meaning confusion or madness — the same root gives durzyć się and zadurzyć się, “to have a mild crush” (a lighter word than zakochać się, “to fall in love”), and odurzony, “dazed” or “intoxicated.” So getting “durnym” with someone during a silly moment isn’t linguistically far from being dazzled by them.