While one prankster dressed as a menacing Jedi rode the elevator, his partner in crime would hit the elevator button to open the closing doors at the exact moment the Jedi extended his hand in an apparent use of The Force.
Riders were quickly freaked outed by the apparently black magic going on. The way the Jedi acted so nonchalantly only added to this effect.
One witness even asked the ‘Jedi’ in question, “Are you Neo or something?”
Another picked up on the gag instantly, offering, “The Force is with you.”