A$AP Relli was the aggressor in his heated exchange with A$AP Rocky and Relli told Rocky to squeeze the trigger on the fake gun he was holding ... at least according to A$AP Twelvyy.

Twelvyy took the stand Friday in the criminal assault trial for Rocky, whose defense team is finally presenting its case.

Rocky's attorney, Joe Tacopina, claims the gun Rocky used to shoot at Relli was a starter pistol firing blanks ...  and Twelvyy says Relli knew it wasn't a deadly weapon.

Twelvyy testified he was smack in the middle of Rocky and Relli's beef, which happened in November 2021 on a street in Hollywood. He told the jury he never saw Rocky point the gun at Relli, much less press it against his stomach or head ... as Relli claims.

The A$AP Mob member even said Relli was the aggressor and dared Rocky to "shoot that fake a** gun."

As we reported ... Relli claims Rocky shot at him and the bullets grazed his knuckles ... and last week he compared his alleged wounds to Donald Trump's ear injury from the assassination attempt.

Rocky is facing two felony assault charges and he's looking at up to 24 years in prison if convicted. He's pleaded not guilty and turned down a plea deal.