4/20 is the high stoner holiday fer sure but where does it come from? Like, what are its origins, where's it comin' from, what's its back story man? Luckily, the day has nothing to do with the Nazi.
There are a lot of theories about how the term 4/20 entered the American lexicon, ranging from Hitler's birthday (which it is but fuck that guy) to the number of cannabinoid compounds present (there are 80) to the traditional teatime in Holland (10am and 7pm) to the date that Jim Morrison died (he croaked July 3rd) with the theories depending on who you ask and how much they've smoked. High Times, however, may have it figured out.
According to Steven Hager, editor of High Times, the term 420 originated at San Rafael High School, in 1971, among a group of about a dozen pot-smoking wiseacres who called themselves the Waldos. The term 420 was shorthand for the time of day the group would meet, at the campus statue of Louis Pasteur, to smoke pot.
"Waldo Steve,'" a member of the group who now owns a business in San Francisco, says the Waldos would salute each other in the school hallway and say "420 Louis!'' The term was one of many invented by the group, but it was the one that caught on.
"It was just a joke, but it came to mean all kinds of things, like `Do you have any?' or `Do I look stoned?' '' he said. "Parents and teachers wouldn't know what we were talking about.''
The term took root, and flourished, and spread beyond San Rafael with the assistance of the Grateful Dead and their dedicated cohort of pot-smoking fans. The Waldos decided to assert their claim to the history of the term after decades of watching it spread, mutate and be appropriated by commercial interests.
The group presented Hager with evidence of the term's use back in the early seventies to corroborate. So there you have it—an entire counterculture's catchphrase was invented by high school kids. [Wikipedia - SFGate - HuffPo]