Take a person with a full head of hair and remove one hair, are they bald? Remove another one, bald? Clearly not, but if you keep removing hairs at some point you have a head we consider bald. Deregulation has been working like that. It's hard to point to one discrete event.

In any case, the process really got going under Jimmy Carter. If we're talking about airlines, I guess you could point to the Airline Deregulation Act. The airline industry had been built in the first place by what people in this thread would call "protectionist" policies.

Stock buybacks are a big part of the story as well. These were illegal market manipulation I think from the Great Depression until the 80's under Reagan.