Puerto Vallarta (PVDN) - April 20 is unofficially World Marijuana Day due to the date being 4/20. The origin of 4/20 as a celebration of marijuana use is somewhat unclear, but it is believed to have started in California in the 1970s among a group of high school students who called themselves "The Waldos." They used the term "420" as a code word for smoking marijuana and would often gather at 4:20 p.m. to smoke together.