sometimes referred to as 'page 78'. When used as 'page 78' it refers to calling someone nerdy.
Note: When speaking of 78 one usually makes the gesture of pushing up their glasses with their index finger. This occurs whether the person wears glasses or not.
Dude! that's 78!
Guy 1: Hey the answer to that is on page___
Guy 2: what did you like read the whole textbook or something? where's the next answer? page 78?
An override code is also sometimes used. This is a predetermined year (post-78) that friends can use to override 78 and reach you in an emergency. The correct usage of the override is to tell the person who is answering "You're no help then; I was talkin to him in 83 (or 84, or whatever you've picked)"
Jeremy (being the only one left, answers the phone): Hello? Greggo? I ain't seen Greggo since '78. Sorry.