Russell Westbrook was LIVID after a fan dumped popcorn on his head Wednesday -- calling the person's actions straight-up "bulls***" -- and even LeBron James is pissed over it all now too.
Westbrook was on his way to the locker room after injuring his ankle during the Wizards' playoff loss to the 76ers in Philly ... when a fan poured their bucket all over the NBA star.
You can see in footage of the incident ... Westbrook could not have been more heated as the kernels bounced off his head -- with the D.