vent one's spleen

To voice one's anger. Mom's been venting her spleen to me for an hour already. Apparently, Aunt Marie has wronged her yet again.

Express one's anger, as in Some people see town council meetings as a place where they can vent their spleen. This expression uses vent in the sense of "air," and spleen in the sense of "anger," alluding to the fact that this organ was once thought to be the seat of ill humor and melancholy. [First half of 1600s]