A nineteen year old daughter of a friend is legally an adult, and the nineteen year old young man in question is an adult also. Both are competent (at least in the eyes of the law) to contract, marry, enlist in the military service, or perform general acts of stupidity in public places. Neither one is under any general compulsion to report or explain their actions to their parents or anyone else.
What would compel me to interject myself into that type of situation?