My 16 year old wee lad has no manners, is irresponsible, lazy and rude. So is my 17 year old wee lass. I've never taught them anything and never corrected them but I expect them to automatically know what to do now. They're still very young though - little kids, they are and I don't know what to do.
MNers: Give them a hug and wait to see if they'll open up. They may be troubled and need extra love and care. If they don't open up, leave them to it, they're still very little and have the right to be little shits. There's still A LOT of time for them to become responsible, well-mannered and polite.