Conor McGregor is FINALLY opening up about why he threw a metal dolly through a bus window ... albeit he ain't the real McGregor ... he's an impersonator.
The guy's name is Al Foran -- and his McGregor impersonation is spot on ... complete with expensive sunglasses and a thick accent ... and he's giving TMZ Sports the perfect take on why the Irish fighter went off in Brooklyn.
"I was just trying to give the dolly over to the Russian," fake Conor says.