Someone who doesn't finish their alcohol before they open a new can/bottle and then doesn't admit that the unfinished drinks are theirs. This results in numerous half-full drinks left lying around.
John: "Who keeps leaving these half-full bottles around?"
Ben(Phantom Sipper): "Not me."
John: "Someone is a phantom sipper!"
Ben(Phantom Sipper): "Not me."
John: "Someone is a phantom sipper!"
by HH_Reezy January 19, 2013