Jon Jones -- I Beat Cormier In the Prime of My Partying ... I'll Beat Him Again! (VIDEO)

Jon Jones says he was "in the prime of my partying" when he beat Daniel Cormier last year -- and now that he's sober, JJ says he's going to beat his ass again.

Jones brought up his partying past at the UFC 200 news conference in Vegas Wednesday -- and in between taking shots at Cormier for being fat, revealed that he's cleaned up his personal life.

FYI, Jones tested positive for cocaine right before his first fight against Cormier at UFC 182. He later claimed he wasn't a coke addict but rather a recreational user who made a "really dumb decision."

Jones says he's now living clean and sober.

As for the fat jokes, Jones said DC has a very "punchable belly" -- and claimed he was having a hard time with the weight cut.

Normally, Cormier responds with smack talk of his own -- but he was unusually subdued this time around ... saying he's sick of of the "jibber and jabber."