I think spanking has its place, but 16 is too old. And now the kid has the moral high ground. If the father had sent the friends home and spoken to the son reasonably, explaining why he wants him to study hard and also explaining how disappointed he was for using studying as a means to show porn (I'm guessing) to his friends, it would have put the son in the bad light. Disappointment always hits harder than spanking ever could.