Wrek, a couple of things come to mind, of course a lot depends on the mother and the type of relationship the two of you have. If she is a decent person, then get on the same page with consequences for your son's inappropriate behavior. He loses priveleges at BOTH homes until he starts showing some respect....cell phone, laptop, television, time with friends, allowances....whatever means something to him....take it away.
Too many times parents think they are helpless, when actually you have a great deal of control. The only things you really owe your children is a meal (doesn't have to be something they like) and a roof over their head. The rest is all extra stuff that you don't have to provide them. You don't have to supply any of the things that entertain them, you don't have to take them out to dinner or run them anywhere.
It sounds like the kid needs to learn that, and also who is in charge.
Also, you may have a harder time if this was a contentious divorce situation. If his mother puts you down verbally and your son hears it. It's not impossible, and probably all the more reason for you to assert your authority over him. Kids really do need boundaries, and will respect parents that set them and are consistent.
Good luck!
