The final press conference ahead of UFC 229 was an unusual affair at the best of times, but it got strange when the Irishman went after opponent Khabib Nurmagomedov's manager in a wild rant.
McGregor and Dominance MMA Management CEO Ali Abdelaziz clashed at the first UFC 229 press conference in New York last month.
Abdelaziz potshotted McGregor for bringing two UFC championship belts to the event, even though he's been stripped of both and Nurmagomedov is the current lightweight titleholder.
McGregor responded that day with some personal jabs and labelled Abdelaziz a "terrorist snitch".
It led Nurmagomedov to later tell ESPN his manager would choke out McGregor if they fought — and when the Irish star was told of those comments at today's press conference he went all in on Abdelaziz.
"His manager is a f***ing snitch, terrorist rat. And that's it," McGregor said.
"I could go into heavy detail ... and I will! I will go into heavy detail.
"He was pulled off of a flight going from Cairo, Egypt to New York City on September 11, 2001. He was caught with five passports in his possession. He turned informant and turned on the people he was working with.
"I don't even know how that man is in this f***ing country. We're all facing — I'm sure all the Irish people here — are facing all this immigration stuff on the way over (to America) ... and then you've got this man with such a crazy background ... and he's walking around free. It beggar's belief to be honest."
Abdelaziz responded with laughing emojis on Twitter.
Later in the press conference, McGregor was asked if he expected Sunday's fight to be the one and only time he'd face Nurmagomedov inside the Octagon.
"I don't know, we'll see what happens," he said. "I'd like to fight Ali. I'd like to fight that rat bastard.
"I may want to spark Khabib and then headline that Madison Square Garden card on November 3 (against Abdelaziz) ...
"Get the promo started — a snitch versus an Irish proper animal."
Nurmagomedov had already left the Park Theatre in Las Vegas before McGregor arrived around half an hour late for the pair's final media availability ahead of Sunday's lightweight championship fight.