In America and Canada, usually coupled with "off", to mean extremely angry. Considered a swear word.

In the UK, Ireland, and Australia, pissed means massively drunk. Generally beyond everyday drunk, a specialist kind of drunk. Not so much a swear word.

that point in drunkeness beyond which you will remember little of what occured the night before

Slight intoxication through alcohol consumption. Typically characterised by a slight sense of drunkenness but none of the more advanced symptoms such as a reduction in inhibitions, loss of self control or inability to respond to questions. One step above sober on the scale of drunkenness and one step below steaming.

Meaning Drunk;
as in piss drunk

This is was orginally a British phase meaning one is either extremely intoxicated or angry, the latter has been adopted by Americans.

off your head drunk, usually aussie, pommy or irish way of saying drunk

adjective
1. Intoxicated; drunk. (chiefly British usage)
2. Very annoyed; angry. (chiefly American usage)

verb
1. Past tense of "piss," meaning "to urinate."