Is on the piss - Idioms by The Free Dictionary
be (out) on the piss (redirected from is on the piss)
be (out) on the piss
rude slang To go out and drink alcohol. Primarily heard in UK, Australia. My friends and I were out on the piss last night, so I hardly remember anything at all.
be on the ˈpiss (British English, taboo, slang) be out at a pub, club, etc. and drinking a large amount of alcohol: I’m not sure if Jerry will be at work today — he was out on the piss with his mates last night.