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Mason Pryor is, no doubt, comedy royalty, but that still didn't save his ass at the legendary Apollo Theater -- and this video of his, umm ... performance ... will totally make you cringe.

Mason, Richard Pryor's youngest son, appeared on "Showtime at the Apollo." As you'd expect, host Steve Harvey gave the 31-year-old comedian the appropriate hype before he hit the stage -- but it was all downhill from there.

You gotta see Mason launch into some Trump-Putin jokes that fell completely flat. The boos rained down, and while some people shouted for him to keep going ... most of the crowd wanted him to get the hook.