Meaning
To get hammered / to drink yourself silly
Example
Ele chapou o coco na festa e só foi pra casa de manhã.
He got hammered at the party and only went home in the morning.
Origin
Coco is colloquial Brazilian Portuguese for the head — the same playful "coconut for noggin" image found in many languages — and chapar means to flatten, squash, or knock flat. Chapar o coco thus pictures drink hitting you until your head is flattened, i.e. getting thoroughly hammered. The related slang chapado ("smashed, high") comes from the same verb.
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More idioms
Acertar na moscaTo guess correctly / To hit the nail on the headAmigo da onçaA fake/false friendAndar na linhaTo toe the line / To behave properlyArmar um barracoTo cause a public sceneRodar a baianaTo cause a public scene / To go ballisticArrumar sarna pra se coçarTo ask for troubleArrastar as asasTo hit on someone / To flirtAbrir o jogoTo come clean / To open upArregaçar as mangasTo roll up one's sleeves / To get to workAgarrar com unhas e dentesTo hold on for dear life / To seize an opportunity