Scott,
I don't think any one person in particular started it, and I know it wasn't around as a rumor until well after he was retired.
The "Randy Savage banged Stephanie McMahon" thing has become a bit of an urban legend in internet circles, but do you know where the story originated? Is it something that just sort of took on its own life as a rumor, or did a specific person/story start the whole thing?
As a random Macho-related bonus, what do you think was Randy's last great match?
I'd call the Flair cage match at Superbrawl 6 his last great one, although the DDP matches in 97 were really really good. We'll just go with the DDP one. Everything after that was pretty worthless, especially once he got into the Macho Pimp era and couldn't hit the flying elbow without breaking his opponent's ribs.