My 18 year old son is a shit bird and I don't know what to do about it.

He usually manages to be at least civil to me, but he avoids me like the plague, refuses to hang out with the family or to come along when we visit people or go places.This past summer he was working a job (which I did want him to get so he'd have spending money for all the fancy things he likes to have - car, clothes, hats eating out ect) that had him out late because he closed every single night. He started staying out even later and hanging out with some kids who had dropped out of school and were living on their own.We went round about it, school started, his grades were immediately in the toilet, and I insisted he cut his hours or quit. He just stopped going in. Great, at least he has time to get his homework in, right? Nope. 9% in the first quarter of senior English.Things settled into an uneasy truce. He did his thing and went to school with me (I teach in the same building he attends) and did football and hung out with the girl friend.Then he turned 18 last week.And he's testing his new adult super powers. Stayed out late last night and has been posting pictures of booze and weed on snapchat. Yelled at me in the hall this morning when I asked him if he'd checked on his final quarter grade in English. (It is apparently my fault he can't make powerschool work for him). HAs been seen in the band room closet making out with his girlfriend and I have kids asking me if he yells like that all the time.I'm not sure what to do to handle this. If I take his phone and car it will be world war three and I am afraid he'll get violent or leave my home. I desperately want him to graduate high school and go do something with himself other than be an asshole who works minimum wage and sponges off people. I also want some basic respect shown to me while I am at work. (I work with special needs kids and I can't even make my own son show respect, what does that say about me?)So, I don't know if this is a plea for advice or a rant. But there it is. My oldest is 18 and an adult and a shit bird to me even while he's all charm and kindness to others.Editing to add because so many asked: The car is not mine. He worked out a deal with a family friend to make payments on it. If he missed the November payment the car will be repossessed as it is still in the family friend's name.I can and probably will be taking his phone and making him delete his snapchat account. via /r/Parenting http://ift.tt/2dy7ZSZ