2 Chainz & A$AP Rocky -- Mile High ... Our 4/20 Made Your 4/20 Its Bitch

When it comes to 4/20 ... rappers 2 Chainz and A$AP Rocky are total professionals, because they spent the "holiday" showing everybody how it's done ... with an epic jumbo joint.

2 Chainz and A$AP were in Denver exercising their rights to toke it up like the world was ending ... with a blunt so big Paul Bunyan might do a double take.

Makes your 4/20 look pretty sad, eh? Don't worry you'll forget all about it ... if you haven't already.