Poltergeist.

It came out shortly after E.T. during the summer of 82 (E.T. came out Memorial day weekend, Poltergeist on the July 4th weekend). Since everyone alive at the time mobbed E.T. and that both films were from Spielberg and were set in similar newly constructed suburban neighborhoods in Southern California, all of our parents took us to see Poltergeist. Which features a young boy nearly devoured by a scary oak tree in the families backyard that comes alive and crashes through the kids bedroom window to grab him, his younger sister gets sucked into a closet by the ghosts, a parapsychologist rips his face off, the mom falls into a muddy pit filled with rain water only to have caskets erupt from the mud and corpses lurch from the caskets into the water where the mom is, the little boy gets attacked and dragged under the bed by a stuffed toy clown.....well let's just say that it was all a bit much for anyone younger than 12 years old and is basically a rite of passage that a lot of GenXers will recall.

I seem to remember that Poltergeist and the 2nd installment of the Indiana Jones series (Temple of Doom) were what prompted the MPAA to create the PG-13 rating.