Conan O'Brien supporters gathered at Universal Studios in Hollywood today -- in the rain -- to protest NBC's mistreatment of their giant, red-headed late night hero.

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The protest -- which gained a lot of support on Facebook -- was set to start at 12 PM PT, but a bunch of Conan's brave, raincoat-clad faithful have been hanging around near the "The Tonight Show" studio for hours.

Jeff Zucker was not one of those people -- but Andy Richter, Masturbating Bear and La Bamba all addressed the crowd.

We're told "The Tonight Show" has handed out doughnuts and coffee to the supporters.