From 1977 and his ill-fated variety show (it lasted exactly four episodes)...
...please enjoy comic genius Richard Pryor as he invents death metal. (Don't blink or you'll miss a shot of Sandra Bernhard in the audience.)
I should add two things.
1) This predates Spinal Tap by seven -- count 'em, seven -- years.
2) That isn't actually the funniest bit from the Pryor show.
Words fail me.