Kids these days...

You interpret in high school and the current trend is for young men to pull their trousers down, exposing their boxers. Your student walks to the front of the class to hand in his work and the way back to his seat--your not looking! But can't help noticing -- he has a hole in his underwear. You look down, shake your head and when your student sits down you tell him to pull up his pants. He shrugs you off as all lame adults tell him the same thing.

Should you
--do nothing. After all, you don't want people to think you were looking.
--tell him about his wardrobe malfunction. After all, he wouldn't want other laughing at him.
--tell the school social worker to tell him. That way it doesn't come from you but he gets the info.