If you got woken early hours of morning by a load of people outside and looked out window and it was one of your friends 14 year old sons would you tell the mother?
Yes as per the others, also I'd want to know whose place not to let him stay over at again if they are able to be out and about that late (unless it wasn't checked with parents, all parents were mislead etc...?). Even so, I'm not sure I'd trust a 15 year old without checking properly with the parents of the lad he was "staying over" with.
There is a school bus stop at the back of my house and I happen to be in the back room getting ready for work while the kids wait for their bus most mornings. Some of the stuff that comes out of their mouths is shocking, and it's alway shouted. They are trying to make sure everyone hears them use the C word, amongst others. If was braver and if I didn't have a niece that went to the same school (and would end up being picked on) I would be temted to take them to task on it. I'm still tempted to call the school about them.