Conor McGregor is firing back at the security guard who claims the UFC star injured him during that crazy 2016 bottle-throwing incident at the Nate Diaz fight presser ... saying his accuser sucks at his job.
The man who filed the lawsuit is William Pegg -- who was working for MGM security on Aug. 17, 2016 ... when Nate and Conor threw bottles and cans at each other during a heated exchange before UFC 202.
Pegg says McGregor chucked a can that struck him in the left shoulder and injured him.