Dewbson-

Here's the wiki version of how we got to this "holiday"


One explanation of the origin of the term stems from a story about a group of teenagers at San Rafael High School in San Rafael, California, United States in 1971. The teens would meet after school at 4:20 p.m. to smoke marijuana at the Louis Pasteur statue. The exact time was chosen because that was the time that afternoon detention was dismissed.

On this day in 1862, Pastuer completed his first successful attempt at pastuerization. Coincidence? Ponder that for a while