Question:
This is hilarious--I have heard from both expatriate amerikans seriously livingin amsterdam, as well as native amsterdam potheads, that 4:20 PM (amsterdamtime)is like the official "pot-break" time of day, there, and has been for a longtime, and THAT"S sposed to be how that got started!

who knows?

Answer: it was a cop call in california (where most of this starts, 187, etc.)for "marijuana smoking in progess." that'd be where 420 came from. it's ain' police code. and it's been used as a sign of rebellion for potsmokers worldwide since about mid '50s i believe.