The one who can open their mouth the widest to take in the largest malescrotum (or teabag). It can also apply to who can suck on a teabag the longest, depending on the context.
Lance and Gary had a contest to see who was the real bagmaster at the party.
A crossbreed between a douchebag and a hipster. A bagster would like the Nickleback, like a douchebag would, and Steve Aoki, like a hipster would. They would also like Kanye West, like both a douchebag and a hipster would. It's okay if you say bagster and someone thinks you said bastard. They're usually interchangeable.
That guy is totally a bagster. He looks just like he got back from a Kanye Westconcert.