Very angry or annoyed; in British English, it also means drunk.
From 'piss,' which derives from Old French 'pissier,' ultimately from an onomatopoetic root mimicking the sound, the word became a general insult around the 1600s.
The fact that 'pissed' means 'angry' in American English but 'drunk' in British English shows how the same word can split into opposite meanings in different regions—linguists call this 'semantic divergence.'
Complete word intelligence in one call. Free tier — 50 lookups/day.