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1.
To take possession of beer left in your fridge for over a week. Typically done with beer left over from a party.
Brad: Dude, where'd my beer that I left from that party two weeks ago go?
Blake: After one week of being left in my fridge I commanbeered it and drank it.

Brad: :(
by BadAirDizzle March 20, 2011
 
2.
To steal or take a person's beer, sometimes done by an aquatic attack
dude I commanbeered so much at the last party i went to

We tried to commanbeer steve, but his friends prevented our attack
by budweiserbro227 April 11, 2010