The word 4/20 comes from a couple of things firstly, a young man (greek) by the names kosta h(btw i hear his hot) or so not sure about his full name invented it by smoking tons of weed euuurddaaay at the same time he noticed a pattern in this. Everyday it would be at 4:20 after school... so from there he new he had to start calling it that. Secondly 4/20 is also a cops way of reporting that ppl are smoking weeed. thirdly, an event in amsterdam (weed capital) at the 4th month of the 20th day of the 4th hour of the 20th minute evryone in amsterdam would smoke the mary-jane.
"hey common lets go 4/20 (ppl dont noe wat it is so lets call it that and wont get caught XD)"
" we have a 4/20 in progress at jane and finch"