If I had a dollar for every time someone told me "it's probably just a phase", or "he's never acted like that at my house", or "have you thought about military school?" - I would have enough money to pay for all the psychiatrist and therapy bills! It's hard not to get frustrated with them and it's even harder not to feel understood.
I still haven't not figured out the right come back for these well-meaning folks, so let us know how you've handled it