I'm not sure what to call this, but here it is.

[CellarDweller]

I agree that this is a part of his upbringing. Have you met his family? It's possible that he has bee exposed to this his whole life.

You need to discuss this with hin rationally, in a calm tone, and let him know how you feel ab0ut this, and that while you understand how frustated he was with what happened, you don't appreiciate how he chose to express himself. You may also want to give him a gentle reminder that if others hear this type of speech from him, it will change their perceptions of him.