Is the 4:20 pot-smoking thing International or is it just East Coast USA?

420 is a "pot head" reference. It was started in the "hippy days" to let everyone know 4:20pm was a good time to start smoking as school was done for the day at this time...

ACTUALLY.. 420 was an old police call sign for marijuana during the 1960's LAPD.. in the 70's people started adopting the callsign as a time, day, event, holiday and all that whatnot