As the rumour goes 5 high school students arranged to meet at 20 past 4 to go and look for an abandoned weed crop in out side of a school named San Rafeal High School there were supposed to meet at a statue called louis they initially used the phrase 4:20 louis... Apparently they couldnt find the missing crop but made a number of searches and eventually shortneed it to 420 and they used that ever since as code to discuess they're weed smoking activities