Monica: I need you at the rehearsal dinner tonight at 1800-hours.
Phoebe: Uh-huh. Okay, what time is that?
Monica: You don't know military time?
Phoebe: Well, I... must've been in missile-training the day they taught that.
Monica: Just subtract twelve.
Phoebe: Okay, so... eighteen hundred minus twelve is... one thousand, seven hundred and--
Monica: Six o'clock!!