Happy National Pot Smokers' Day! Actually, it's probably illegal to celebrate it here, so maybe just dream about that beer you can now have at an Indiana State Fair concert.
I heard somebody on the radio say that nobody really nows how 4-20 ever became associated with marijuana smoking, which is the kind of thing we used to have to accept at face value, but in the Google era, we can kind of look that up ourselves. I found all kinds of stories about the supposed origin, one that occurs more frequently than others. That, of course, requires a visit to snopes.com, whose word I will take at face value:
Odd terms sneak into our language every now and then, and this is one of the oddest. Everyone who considers himself in the know about the drug subculture has heard that '420' has something to do with illegal drug use, but when you press them, they never seem to know why, or even what the term supposedly signifies.
It's both more and less than people make it out to be. '420' began its sub-rosa linguistic career in 1971 as a bit of slang casually used by a group of high school kids at San Rafael High School in California. '420' (always pronounced "four-twenty," never "four hundred and twenty") came to be an accepted part of the argot within that group of about a dozen pot smokers, beginning as a reminder of the time they planned to meet to light up,4:20 p.m. Keep in mind this wasn't a general call to all dope smokers everywhere to toke up at twenty past four every day; it was twelve kids who'd made a date to meet near a certain statue. It's thus incorrect to deem that '420' originated as a national or international dope-smoking time, even though the term began as a reference to a particular time of day.
The post also has most of the myths about the origin, including the "fact" that it's the penal code for marijuana use in Californioa and that it is the date that (take your pick) Jim Morrison, Jimi Hendrix or Janis Joplin died. Snopes also says the term has "slipped into a position of semi-respectability."