Girl At Party: Dude, you can't just start a slow clap at any time and expect everyone to join in. You have to wait for the right moment.
Guy At Party: Oh, okay... But h-how will I know when its the right moment?
Girl At Party: Oh don't worry, you'll know.

The first recorded instance of the slow clap is right after Jesus brought Lazarus back from the dead. Saint Peter just thought it was the most appropriate thing to do.