Well, he is definitely manipulative and abusive, physically and emotionally...and acting out inappropriately.. I'm sure the alcohol abuse isn't helping any. Whether or not he isin psychosis is up in the air unless someone actually asks him. It doen't sound like he is very cooperative. So, if he wasn't your friend and a complete stranger, what would you do?
If you want to help him, without enabling him, and before he gets in touble with the law or harms someone, then alert someone about it. I don't know if you are in the US or out in a remote area, but if you don't have a mental health crisis response unit or a crisis hotline in your area. Otherwise, it ill be a given that the police will get involved one way or another. Stealing, sexual harassment, and battering isn't really something a good friend would do. Even if he is mentally ill, that still isn't acceptable behavior in or out of a hospital.
I am assuming you are all legal drinking age for your state or country, but guessing you are adults with not much life experience. Check on the entl health resources in your area to find out what to do if you really want to effectively help him. However, you should know that the first rule for anyone who helps another is to make sure you are safe and not in a vulnerable position of being harmed or endangered. You don't have any clue what is going on in this fellow's head, and he already demonstrated that he doesn't really care what happens to others.
If it is over your head and you aren't capable or knowledgeable about dealing with a behavioral crisis situation, talk to someone who is physically there in your area who can advice you on what to do. It can be police, paramedics, hospital, a crisis intervention hotline, a mental health resource or support group, a pastor, priest, rabbi, etc.
If you are all underage, then talk to your parents, school counselor, someone in the college clinic, etc. It is going to feel very uncomfortable intervening, btw, and I am pretty sure he will most likely tell you off.
Regardless of age, knowledge and experience level, safety first. whatever action or inaction you take has consequences, so you need to know what you are getting into and know exactly what you are capable of handling. Btw, it isn't anything like what it is in movies or television...those portrayals get edited for a good story.
Wow, I dont think your friend has BPD. Possible symptons of Bipolar I, but more Psychosis in my opinion. Sounds like he really needs some type of help, especially if he is a danger to himself or others. Have you attempted talking to his parents? x
This doesn't specifically sound like either to me. Sounds like a guy who is emotionally in trouble. There may or may not be something going on mental health-wise, but only a professional can diagnose him.