I have a 17 year old boy at home and a 13, I told them I know you swear but what you do with your friends is between them, but I will wop your ears in if your caught swearing in front of children, women or me.
A parent can only do so much but encouraging it is a definite indicator the adult has mental issues, and possibly a limited vocabulary. As I tell my boys wit and sarcasm can only be accomplished with intelligence. Any dog can cuss.