Who? Jackass star and his then-girlfriend.
Real? Yes, it was released officially as an easter egg on the CKY4 DVD.
Daze Reader wrote about the Bam Margera sex tape in November 2004:
Rumors of a Bam Margera sex tape have popped up in the last week. The footage really does exist and has been in circulation for almost two years, originally as an “easter egg” on the CKY4 DVD. It’s just a short clip, under two minutes, in washed-out black-and-white and slow-motion, showing Bam Margera and girlfriend Jenn Rivell in assorted positions. Cinemaxesque softcore, no genitalia on display.
This makes it one of the few celebrity sex tapes officially released by the celebrities themselves.