2 Chainz -- CRAZY VIDEO of Rapper Being Robbed at Gunpoint

TMZ has obtained EXPLOSIVE VIDEO of 2 Chainz and his crew being robbed at gunpoint in San Francisco this weekend ... and the footage shows the chaotic moments as the rapper and his crew desperately ran for their lives.

2 Chainz and his entourage were casually walking down the street Sunday afternoon when at least 2 men approached the crew and pointed guns at them ... one in a white shirt, the other in a black hoodie.

2 Chainz and his crew immediately scattered -- frantically trying to sprint down the street while the gunmen chased after them.

One of the gunmen seemed to be having fun during the incident ... and gleefully skipped after the rapper while 2 Chainz tried to get away.

During the chase, 2 Chainz stumbles and falls ... and one of the gunmen pounces ... hovering over the rapper with his gun drawn.

According to police, the bad guys jacked 2 Chainz for his cell phone and wallet. Towards the end of the video, you can see a man running back up the street with what appears to be the loot stuffed under his clothes.

Under the category: "Who ya gonna believe, me or your lyin' eyes" ... 2 Chainz later posted a tweet denying he was robbed ... saying, "Rule #1 if a rapper gets robbed people usually post items that has been taken."