R. Lee Ermey -- Geico FIRED ME for Bashing Barack

Ever wonder why R. Lee Ermey only did one hysterical commericla for Geico? The "Full Metal Jacket" star says the insurance giant gave him a pink slip because of his political beliefs.

Ermey famously bashed President Barack Obama in December 2010, saying his administration was trying to "impose socialism" on the American people and was "destroying the country."

He apologized at the time for those comments, but the other day he told our photog that Geico fired him over the incident. He explained, "If you're a conservative in this town, you better watch out."

But R. Lee showed he's capable of backin the Prez when it's called for ... calling Megadeath frontman Dave Mustain's theory that Obama staged the shootings in Aurora "ridiculous."