piss sip
Piss sip is the very end of a drink, usually a shitty frat beer but could be anything. Not a desirable last sip and usually warm. Most beers at end of a party have a little piss sip left.
"Dude are you gonna finish this beer?"
"Nah. It's just the piss sip that's left."
"Nah. It's just the piss sip that's left."