"Puneta" (often spelled puñeta) is a highly offensive vulgarity in Puerto Rican Spanish. It derives from the word puño (fist) and refers explicitly to the act of male masturbation. In colloquial usage, it functions as a versatile, aggressive insult roughly equivalent to "motherfucker," "asshole," or "jackass" in English, though its literal sexual connotation makes it significantly cruder.
This word is strictly informal and taboo in polite company. It is avoided in professional settings, media (unless quoting), around elders, and in mixed company. Using it signals high aggression, extreme familiarity, or a deliberate breach of decorum. It is not a word a visitor should attempt to use; misunderstanding its severity can cause serious offense.
For context, milder Puerto Rican expressions for frustration include ¡Diantre! (Darn!), ¡Coño! (Damn! — vulgar but less so), or ¡Mierda! (Shit!). Puneta sits at the far end of the vulgarity spectrum.