Antonio Brown had a REALLY good 4/20 ... the dude smoked a footlong blunt -- and then rapped for a huge crowd in downtown Los Angeles!!!
AB was out in DTLA on Wednesday night for Gunna's new weed strain launch event -- and the free agent wide receiver was having the time of his life.
TMZ Sports got video of the 33-year-old smokin' weed and then hitting the stage to perform songs off his new album, "Paradigm" -- which a packed crowd in attendance loved.
In video from the event, you can see Brown smoked several times (including once from a monster blunt) in between grabbing the mics -- and at one point during one of his songs, he even threw a bunch of money at the crowd.