Hi! You know, to give you the best answer, I think I should ask you a few questions first that will help define the problem and the situation.
It's certainly a sign of a mental disorder. HOWEVER, I don't yet know if he's doing this on purpose or if he is being driven by a disorder to behave that way. For example, he could be hiding his drug use by being aggressive to get you to back down.
Either way, this type of behavior doesn't just come out of the blue. What's the history here?
What has he been like up to this point?
Has he had any mental health issues?
Is he getting any treatment right now? If so, what type? How is it going?
If not, when was the last treatment? What type of treatment was it? Was it helpful?
Any extra information that will help, feel free to share.