If you’re taking flak, chances are you’re in a bad situation and taking fire from an enemy. Flak can refer to criticism — or worse, explosive shells from an antiaircraft weapon.
Flak came into English as an abbreviation for the German word Fliegerabwehrkanone, meaning 'aircraft-defense gun.' (Yikes! No wonder they abbreviated it.) If you’re dealing with a lot of flak, you’re either in a fighter plane over enemy territory drawing shots, or you’re dealing with a volley of criticism that seems like antiaircraft fire. If you show up late for work for a third day, you’ll probably take some flak from your coworkers — they’ll take verbal shots at you.