The slang "going postal" kind of slipped in under the radar if you ask me.  What was a topical item in the 90s, is now just another idiom.  I actually can't help but feel bad for the united states postal service.  I can't think of anything they've done in recent years to preserve the meaning of the phrase.  Maybe in 20 years from now, people will have to explain the origins of "going postal."