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1 definition by sobieski

 
1.
Flak, from the german "fliegerabwehrkanone", originally referring to land-based anti-aircraft defense systems, has more recently been used when speaking about low velocity shrapnel-based war-time technology (ie the 'flak jacket' etc).

Figuratively, this phrasing is used to allude to broadly targeted aggressive interpersonal behavior.
'he was feeling insecure and start shooting off a bunch flak without realizing she was the one getting hit by most it, what a careless bastard'
by sobieski November 21, 2009