420

1. Some sources, including The High Times, claim that in the early 1970s, a group of teenagers at San Rafael High Schoolin San Rafael, California used to meet every day to smoke marijuana after school at 4:20 PM at the water tower. 
2. The California police code describing people who use, eat smoke or sell cannabis.
3. In Doctor Hoffman's chemical tests, LSD was first injected to a human was at 4:20 PM (Wow!).
4. People once believed Marijuana has 420 different chemical substances in the plant itself.
5. Bob Marley - a famous Rastafarian reggae musician, passed away on the 11/5. For some reason , people believed that he passed away on the 20/4.
6. Adolph Hitler is also linked to the 420 culture stories. He was born on the 20/4 and died on the 30/4.
7. 4/20 is the last day of the year on which you can plant cannabis seeds (yeah, right).

There are many expressions of 420, in literature, radio, TV, cinema, music, and many pop culture events:

1. 2 Beatles songs (one of them is "Smoking", the other "Come Together") are 4:20 length. There are several other songs which are 4:20 long by The Doors, The Grateful Dead, Led Zeppelin and Green Day.
2. "Doobie Time" is a time to smoke marijuana in the cannabis slang. D is 4 and T is 20 (uh... what? I didn't write that).