For several years, since Melendez reigned supreme over the Strikeforce lightweight division and Eddie Alvarez was Bellator's head of the class, the duo have taken swipes at one another like rappers dropping diss tracks.
Alvarez would launch a verbal grenade at Melendez in the media, trying to goad him into a unification fight. Melendez would pretend to brush it off, then lay the verbal smack down, launching an Alvarez rebuttal, and so on.
Round and round the verbal jousting would go, with both fighters alternately claiming not to care what the other thinks, then making statements about what would go down if they ever tangled.
Even now, with a fight five years in the making finally at hand, in the co-main event of UFC 188, the duo both try to claim the fight isn't all that big a deal, right before verbally tearing into one another.
The thin layer of indifference barely masks a deep well of contempt, a real grudge in an era of endless hype, the ante raised by the bragging rights for the winner between a pair of Latin American fighters competing in one of Latin America's combat sports capitols.
"I don't know Gilbert enough to say I have anything personal against him," Alvarez said at Thursday's UFC 188 media day, sounding more like he was trying to convince himself than others. "He seems like a nice guy, he has a family, he has a daughter, a business, I respect guys like that."
It's as if Alvarez is setting up the pins just to knock them down.
"It's just, some things he said in the past that pissed me off," Alvarez has said. "And anybody who calls me out, it's hard for me not to take it personal. It's hard for me not to think that that guy thinks he can beat me. And, you know, we just have separate beliefs, so you're going to have some type of argument when that happens."
Melendez, likewise, tried to play off like the Alvarez feud was no big thing, before claiming Alvarez was the one who started it all.
"I would engage more if it was, like, intelligent trash talk," Melendez said. "But he says inappropriate stuff that, I don't even want to get into that."
Melendez then gets right into it.
"I just think that, you know, over the years, he's a very great fighter, he is," Melendez said. "But I don't think he's the brightest human being at times. He hasn't made the best decisions over the years, with his career, with his contracts, and I think he's a little salty at times."
What started out as a King of the Underground-type battle, the fight hardcore fans wanted to see between the two lightweights most thought were the best outside the UFC, took a right turn after both ended up in Zuffa.
The way Melendez sees it, Alvarez's hate boils down to a case of envy. A couple years back, Alvarez thought he was coming into the UFC with PPV points and a title shot. That was before the legal battle with Bellator which kept him on the sidelines. Melendez, meanwhile, played Bellator to get a great deal from the UFC, one which included a title shot.
"He was supposed to fight for the title against Benson Henderson," Melendez said. "He had the UFC contract, and Bellator just erased the ‘UFC' and put ‘Bellator' on top and matched it. He threw a hissy fit because he thought he had a handshake deal, but we all know that it's about on paper, and it's about what's signed. Next thing you know, he doesn't have a title fight, and I do. So he's pissed off about it."
Alvarez, unsurprisingly, denies the charge.
"I rarely get emotional about much," Alvarez said. "If I get emotional in any way, it's that I get overly excited. I don't get down and out, I don't get angry too much. Gilbert's going to say what he's going to say and that's that."
Even if you stripped away the authentic personal animosity between the two, you'd still be left with one of the most consequential contenders' fights the UFC has put forth in quite some time.
Both fighters are at pivotal career junctures.
Alvarez came out flat in his UFC debut, looking slow in his unanimous decision loss to Donald Cerrone at UFC 178. Some said it was ring rust. Some said his best days are already behind him. Those latter voices will only grow louder if he can't put on an impressive show against Melendez.
"You know, my goal here is to win the lightweight title," Alvarez said. "Since my fight with Cerrone, fans, promoters, media, whoever, they all think I'm a has-been. I'm the same person I always was. So, to help ease the pain of my first loss, this will put me right back on track, to be there in the top three."
Melendez, meanwhile, is in the dread no-man's land of being in a weight class in which you've come up short in two title shots. Melendez knows he needs the victory to stay near the top of the pack. He also knows that with the title being passed around like a hot potato, and with injuries to top stars, a third title shot isn't as far-fetched as it may seem.
"Timing is everything in this sport," Melendez said. "One win after this fight here and I could possibly get another shot, if the timing works out. [Anthony] Pettis is injured, Khabib [Nurmagomedov] is injured, who knows? What if Cowboy [Cerrone] gets injured? You don't know. I may be a long ways away. I want to stay relevant and prove I'm one of the best in the world."
It's rare such that a hardcore dream match is put together while both fighters are still relevant. Rarer still when both have reputations for delivering crowd-pleasing bouts. Even more rare to also involve cultural bragging rights.
Gilbert Melendez vs. Eddie Alvarez the fight which has it all. The personal animosity is the icing on the cake.
Even if neither fighter cares to admit it.