As you may have already heard, that scene in "The Champ" when T.J. (young Ricky Schroder) weeps over his father (Jon Voight) Billy's body after a boxing match turned fatal is the scientifically proven saddest movie scene ever.
Science wasn't necessary to prove this. Old Yeller was a dog. Bambi's mom was a cartoon character. And Vincent Schiavelli made "Ghost" funny. But whatever; the death of the Champ isn't quite as sad when you watch kids acting the scene out in some depraved school assembly.
The Saddest Movie in the World [Smithsonian]
The Champ Death [YouTube]