How did you deal with your son's negativity and hostility as a teenager?

Something is bothering him. If this is a big change in personality, its not "just something he's going thru". When children go through their teens, the brain makes changes. This is why so many young college students have their first schizophrenic episode. I would definitely see if you can find a way to talk to him or get him some counseling. It could be drinking or drugs or any number of other thing but I'd not just chalk it off to being a teenager.