The act of opening the anal cavity to allow a group of 10+ strangers to urinate, deficate & ejaculate into the ‘arse keg’. The ‘arse keg brew’ is then allowed 10 minutes to settle, before being serving to the group of participating strangers to sip and enjoy through a straw.
“Hey have you seen Daisy?”
“Yeah, she’s in the corner being the Arse-Keg’”
Or
“Hey, are you down to party tonight?!?”
“Damn right, I wouldn’t miss an arse keg party!”