A brew bro is any guy with a lifted truck and a famous shirt.. usually from the 909 or I.E. but they seem to be popping up everywhere now. They're called brew bros because thats the way they ask for a beer.
909 guy: Hey Taylor, can you pass me a brew bro
Taylor: What kind ? Natty or bud light..
909 guy: Who cares, just pass me brew bro