"Somebody just walked up and hugged me," Diaz recalled. "I figured I know this person, I live in a small town. Then it was like 'I don't know this person at all.'
"I've got to deal with that."
The 31-year-old bad boy from Stockton, Calif., wasn't really complaining. Pressed on the issue, he conceded the happy stranger was a "nice guy" and "a huge fan."
"He gave me the hug first before he told me that," Diaz said with a laugh. "But he was really excited, he really was a big fan. And I appreciated he wasn't weird or nothing. He was just a fan."
It speaks volumes about Diaz that the former Strikeforce champion attracts such a following despite often refusing to play by the rules and showing a snarling persona rather than a smile.
There are two kinds of Diaz watchers: those who applaud his "I don't give a damn attitude" and those who tune in hoping he will have the trash talk beaten out of him by his opponent.
For the UFC, that's two fan bases in one and helps explain why it keeps going back to what amounts to a six-foot walking headache.
UFC president Dana White was reaching for the aspirin again this week when Diaz failed to show up for a public workout session Wednesday ahead of his UFC 183 showdown Saturday with former middleweight champion Anderson Silva.
It's the first fight for the 39-year-old Silva (33-6) since he suffered a gruesome leg injury in a loss to title-holder Chris Weidman at UFC 168 in December 2013.
Diaz (27-9-1) had elected not to get on his scheduled flight, the UFC later explained. The fighter landed in Las Vegas later Wednesday but not before White tweeted a photo of a milk carton with Diaz's face on the side.
White said this week that a film crew dispatched to Diaz's home for the "UFC Embedded" video series had been unable to find him.
This is a fighter who was pulled from a UFC 137 title bout with then-welterweight champion Georges St-Pierre after refusing to show up for press conferences. He once brawled with fellow fighter Joe (Diesel) Riggs in the hospital after their UFC 57 showdown.
Diaz has also been suspended twice for positive marijuana tests. Diaz told the Nevada State Athletic Commission after the most recent failed drug test that he had been prescribed a medical marijuana card to help deal with his ADHD (attention deficit hyperactivity disorder).
When Diaz did fight St-Pierre at UFC 158, he showed off his chatty side by launching into a stream of consciousness monologue of which White later said "(In terms of) craziness, that was a 10 out of 10."
"He is a fascinating human being, very tough to figure out," White added. "What most people care about, he does not. He's a very unique individual."
Younger brother Nate is equally abrasive. His signature win involved flexing his muscles and displaying two middle fingers while opponent Kurt Pellegrino was locked in a triangle choke.
After losing to GSP, Nick Diaz had reporters and White shaking their heads when the fighter confessed: "I've never paid taxes in my life, I'm probably going to go to jail."
Diaz, a black belt in jiu-jitsu with slick boxing skills, has also admitted he doesn't much like fighting for a living.
"It's pretty rough. I don't recommend anybody to be a fighter," he said last July. "Fighting is not something I enjoy doing. It's something I do that I feel I have to do and that's just the way it is."
"I don't like to hurt anybody,'' he added. "I'm a non-violent person."
And yet when he is in the cage, he usually belittles his opponents with a torrent of trash-talk.
Diaz, whose workout regimen includes triathlons, has fought at both welterweight (170 pounds) and middleweight (185). He says he walks around at close to 200 pounds and that making 170 has been "pretty rough'" in the past.
For all his quirks, the "UFC Primetime" show before his UFC 143 fight with Carlos (The Natural Born Killer) Condit showed Diaz as a loyal, single-minded athlete willing to dispense with the social niceties in search of excellence.
Diaz often said he wants to be known as someone who "who kept it real." But he does it while travelling a bumpy road.
"Like my life's a mess,'' Diaz said in March 2013. "I'm not afraid to admit it."
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