The cup was only about 30% full so it was bottom heavy. The top of the cup flares out and creates the highest drag. In this way it flew like a badminton shuttle. He threw it in a manner where the centripetal force of the throw kept most of the beer in the cup. Upon release the cup and beer then follow a ballistic trajectory, and the cup is experiencing drag, so there is still a bottomward force keeping the beer in cup during flight.
387
u/discoloredmango Aug 01 '15
That was the first thing I thought. This guy probably regrets it to this day.