The duo arrived nearly two hours late for the performance.
McGregor sported a large fur coat with a snake on the back when things finally got started at the Barclays Center. Mayweather wore his familiar TMT garb.
The Irishman repeatedly took the coat off and put it back on, wearing only his loafers and paisley-styled pants.
"Money" Mayweather entered the stage with an Irish flag draped over his shoulders. He tossed the flag onto the stage floor, before dancing weirdly in front of his opponent.
The duo then lined up for an intense stare down. McGregor threw his coat off again and got inches from Mayweather's face.
The crowd chanted: "Pay your taxes," referencing Mayweather's unresolved issues with the IRS.
UFC president Dana White and Mayweather's team quickly separated the fighters.
Tickets for the Aug. 26 mega fight in Las Vegas' T-Mobile Arena go on sale on July 24.
"It's the, N-O, T-O, R-I, O," McGregor said, referencing lyrics from The Notorious B.I.G.'s Going Back to Cali. "U-S, you just, lay down, slow. Recognize a real Don when you see one."
He began the presser by saying "50 Cent is a [expletive]."
50 Cent later responded to the dis.
"What the [expletive] wrong with this white boy, you fighting Floyd not me fool," he wrote on Instagram.
McGregor presented Mayweather with Jay Z's new album.
"I got Floyd a gift," he said. "This is Jay Z's new album 4:44. I want you to take this, listen to it and learn. Learn how to build and maintain a real empire, not a fake empire. And when you're done with it, send it on to 50 [Cent]. And when you do, tell him Blanco sent ya."
"The Notorious" has offered some cringe-worthy thoughts on the world tour of news conferences, referencing race among other things. He addressed those statements, made in Los Angeles and Toronto, to the crowd of more than 13,000 fans in New York.
"Let's address the race," McGregor said. "A lot of media is saying I'm against black people. That's absolutely [expletive] ridiculous. Do they not know I'm half-black? I'm half-black from the belly button down."
McGregor also called Showtime's Stephen Espinoza a "weasel," before telling him to turn the air conditioning up.
"The coat is polar bear. I'm a cold [expletive]," he said. "[Expletive] you. Do something about this polar bear coat I've got on. Somebody stop me from walking around this place like I own it. I don't give it a [expletive] how hot it is outside. I'm still wearing this [expletive]."
"I don't just smell victory," Mayweather said. "You know what I smell? I smell a [expletive]."
He then told the crowd to point to the quitter [McGregor].
"Money" proceeded to toss hundreds of bills into the air, making it rain on McGregor. His counterpart revealed that all of the bills were $1 bills.
After the cash shower, he told his entourage to "form Voltron." A small scuffle broke out when all of the men surrounded McGregor.
After the presser, Mayweather talked about the disrespect his opponent showed during the news conference.
"He disrespected my daughter, disrespected the mother of my daughter," Mayweather said. "Disrespected black women. Calling black people monkeys. It's totally disrespectful. I have a diverse team, diverse staff. And when I was young, I may have said some things that I shouldn't have said when I was young. But we live and we learn and we don't say those things once you get to a certain age."
"You do not disrespect, I don't care if its white women, black women, white men, black men, Asian, Latina, or Latino. You don't disrespect people," Mayweather said.
On Wednesday, McGregor coach John Kavanagh referenced Mayweather's history of domestic violence.
"He should have stuck to hitting girls and running strip clubs. He's awoken a dark, dark animal that he's only met in his worst nightmares," Kavanagh tweeted.
Thursday's presser had audio issues that made it hard for fans to hear the words the fighters were saying. The show was so bad that White apologized on social media.
"Thank u so much Brooklyn, NY!!!! So sorry about the [expletive] show," White said on social media. "It's not my show or it would be run WAAAAAY different. Thanks for always supportin."
The Aug. 26 bout in Las Vegas is 42 days away.