April 20 or 4/20 is now commonly known as 'Weed Day' (Marijuana Day for you hipsters), but why?  Well, here's what I found out.

According to cute-calender.com:

The earliest use of the term began among a group of teenagers in San Rafael, California in 1971.

The group first used the term in connection to a fall 1971 plan to search for an abandoned cannabis crop that they had learned about.

They designated the Louis Pasteur statue on the grounds of San Rafael High School as their meeting place, and 4:20 PM as their meeting time.The group referred to this plan with the phrase "4:20 Louis".

Multiple failed attempts to find the crop eventually shortened their phrase to simply "4:20", which ultimately evolved into a codeword that the teens used to mean pot-smoking in general.

Well there ya go then...