Longer (and juicier) answer: rabat-joie has cousins—casse-ambiance, casser / plomber l’ambiance, and, if you’re feeling très old-school spicy, pisse-froid (careful: that one’s fam. and a bit… splashy).
I learned this the hard way. I once tried “couverture mouillée” and my baker looked ready to offer my blanket a spin cycle. Moral: keep laundry at the laverie and idioms in the café.
The quick cheat-sheet (with vibe check)
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Un/une rabat-joie — the classic “wet blanket” (a person).
“Ne fais pas ta rabat-joie ! On va danser quand même.” -
(Un) casse-ambiance — colloquial; the human equivalent of a DJ pulling the plug.
“Quel casse-ambiance, celui-là.” -
Casser / plomber l’ambiance — the action: to kill the vibe.
“Il a plombé l’ambiance avec son mail sur les impôts.” -
Pisse-froid — archaic/fam.; delightfully tart, deploy with care.
“On n’invite pas le pisse-froid cette fois.”
Mini dialogue (A2-friendly)
— On sort ce soir ?
— Oui ! Et pas de rabat-joie, d’accord ?
— Promis. Je ne plombe pas l’ambiance… sauf si on parle de préfecture.
(See? Even I can learn. Slowly. Like my passé composé.)
What not to say
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✗ couverture mouillée — That’s just… a damp blanket. Useful after mistral-powered laundry, not at parties.
If you’re French and reading this: merci for tolerating our aquatic metaphors. If you’re a learner in Aix: pop “rabat-joie” in your pocket, and the next time someone rains on your rosé, you’ll be armed with the perfect, perfectly French eye-roll. Pas besoin de sèche-linge.