if you don't want to torture yourself by watching this, just read the recap here. choice excerpt:
The gunman takes turns pointing the gun at different people’s heads until Peter (who happens to be in the store) shouts at him that he’ll have to answer to God. Then he volunteers to take the bullet: “If you’re going to shoot someone, shoot me!”
The gunman considers it, but then grabs the girl from the straight couple and drags her out of the store with his gun to her head. The police have shown up. He won’t let her go!
That’s when Peter saves the day: He eyes a can of spinach in the store, walks up being the gunman, and clocks him in the head with it.
Peter is a hero, and he takes a series of selfies as the gunman sits in the police car.
there's also something about how not telling gay people they're doomed is just like taking a sign off a malfunctioning elevator and letting unsuspecting people get in and fall to their deaths.