The act of taking and drinking other peoples drinks that have been left on the side of the dancefloor or the bar. It is also acceptable in bargain hunting to take peoples drinks even if they are there, but they are looking away. It is often followed by exclaiming 'barrrrrgain' and downing the bargained drink.
"I only spent a fiver last night, i was bargain hunting all night!"
"BARGAIN!" (After bargaining a drink)