Human aggression doesn't have much going for it. Every war, bar brawl or playground smackdown ever fought has resulted from our habit of lashing out first and talking it through only later. But if aggression has one virtue, it's that it's unambiguous. It's hard to misunderstand the meaning of a missile launch or a punch in the nose.
But passive-aggression — regular aggression's sneaky little cousin? That's a whole other thing. Passive-aggression is there but it's not, you see it and you don't. It's aggression as steam — hard to frame, impossible grasp. You see it in the competitive colleague who would never confront you directly but accidentally leaves your name off an email about an important meeting. It's the spouse who's usually punctual but takes forever to get out of the house when it's your turn to choose the movie. Sometimes there's an innocent explanation, but often there's not — and the passive-aggressors themselves might not even know which is which.