A glass/cup/mug of beer that comes from multiple pitchers over the course of the night, and which is of questionable origin.
Tommy: I started out drinking Molson, but I've poured so much other shit in this bastard beer that I don't know what I'm drinking.

Michael: Yeah, (holds up glass of orange/yellow beer) I started out drinking Guiness...
by tinydancer88 March 7, 2010
Get the bastard beer mug.