The universally accepted time to smoke marijuana. Began when a group of high schoolers in the '70s from San Raphael High School in California decided to meet up every day at 4:20 to smoke.
"They had just bough a sack weighing 3.5.
It was 4:19, just about that time. i.e., almost 4:20 They pulled out the binger and I started to drool.
It was the five-foot caustic weapon crystal, too.
I caught the fumes and I lost my mind,
Happens every time that I smoke the kind."
-Wasting Time, by ALO