Sloper
The half filled drink cups and beer bottles left on the sidelines at a party. Term refers to the way you have to tilt the bottle to the side in order to see if there is any liquid in it.
Dude, the keg is kicked! Just grab one of the slopers over there on the windowsill.

I was cleaning up after the party and someone left a bunch of slopers on the table. Most of 'em have cigarette butts in them too.