You don't say why but I just read someone's question about how to get rid of her sons mother, who was terribly invasive Don't be that person. The best way is to let your son choose and learn to make his own mistakes. Another good thing to do is keep your friends close but keep your enemies CLOSER, which means be nice to her and pray he will be man enough to make good decisions on things that affect him negatively and better decisions on things that affect him positively, through your parenting skills.
You don't. You have to let your son make his own mistakes and learn from them.