what is the concept of 420 4/20 4:20 ???

[beachguy in thongs]

I go for this one: April 20 is the last day on which one is supposed to plant cannabis seeds.

Or,

The Bob Dylan song "Rainy Day Women #12 & 35" is informally known as "Everybody must get stoned" since the chorus repeats that line. 12Ã?35=420.