Chuck vs Tito: Often times fighters are said to "genuinely dislike each other." The fact that that statement needs to be clarified to the public implies that many of the pre fight antics of fighters trash talking is not genuine. But I think Chuck and Tito was the real deal.
When Chuck was in the peak of his prime, Tito actually tried to claim they were friends and so he wouldn't fight Chuck for the title. Chuck responded "I'm not your friend." And a war of words began, but then suddenly Tito was injured for like ever. So Chuck fought old man, semi retired Randy for an interim belt. To everyone's shock and Amazement, Randy won.
Suddenly Tito felt better and defended his belt against Randy. Well, tried to defend it, but got spanked. So when Chuck Finally got the belt, there were no more antics Tito could do to avoid fighting Chuck if he wanted the belt back. And Chuck just whipped him.
After two embarrassingly outclassed losses to Chuck and Randy, it looked like the sport had passed him by. Many assumed Tito was done. But Tito went on to win 5 straight. At the time people saw this streak as being highlighted by wins over Shamrock. In retrospect, the wins over Vitor and Forrest were the real proof he still had gas in his tank.
But Chuck was wrecking shop. Since beating Tito, he had strung together 5 title defenses all by T(KO). Tito had technically earned a shot, but few believed it would go longer than a round. While Tito ultimately lost, to the surprise of many, he gave Chuck a competitive fight before finally succumbing to shots in the second.
Final proof that their rivalry was "genuine" is that post fight, Chuck still reports he doesn't like Tito.