Not so interesting- fallacious irrelevancy

You can be unambiguously, unsubtly clear without going on the attack.

I certainly would not argue for passive-aggressive behavior; be clear, but don't be rude.

Perfectly reasonable, unambiguous responses to bad code or even bad patterns of behavior from a contributor:

"I don't want to see code like this ever again."
"Don't ever break userspace. Ever. It's never OK."
"I'm seeing the same set of mistakes in many pieces of code from you; please understand the problem better before sending any more patches."
"You should know better than this."