Jon started the latest round ... taunting Cormier on social media for failing to accept the "truth" that PEDs had nothing to do with JJ's two victories over him.
Jones says the U.S. Anti-Doping Agency has backed his claims that he didn't intentionally ingest any prohibited substances ... and insists Cormier simply can't come to grips with the fact he's the superior fighter.
Enter Cormier ... who fired back on social media Friday morning.
"So here we go again Jonny boy. First off, if you did nothing wrong and were 'innocent' then you’d have never been suspended," Cormier said.