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1.
A name you call someone when they're acting like an asshole, but they are still your bro even if they're a jerk.
"dude, Dain stop being such a brosack, k bro?"
by theOctYatVlog April 06, 2010
 
2.
a guy whos usually a bro, but being a jerk at the present moment.
"Wow, Jeff's the man, but he just totally just d-blocked you"
"Ya, what a brosack."

by Dj Gj January 11, 2009
 
3.
A Pull String Backpack
Liz: Man I am so bro sporting my brosack.
by staybro12345 December 08, 2010