They called it the acting game.
I only played it once, Johnson admitted, before explaining the rules.
You get a fake scenario and answer the phone and act out the scenario.

Credit: Andrew Lipovsky/NBC
Hi babe, Johnson said upon answering the fake call.
Did you just wake up?
After the fake Darth Vader explained where he was and who he was with, Johnson became angry.
she said, stopping short because Johnson realized she just cursed on national television.
Laughter and even some tears ensued.
(SinceThe Tonight Showis pre-taped, Fallons producers bleeped the swear out for maximum effect.)
Things calmed down slightly from there, at least on the expletive front.
Watch the very funny segment below.