Come on guys, you know boxers do that to hype up the gate. Let's be honest, nobody wants to see two boxers over a cup of tea discussing their bout together. They want to see wars like Ali vs Frazier.
Usually after a fight is over, both boxer's praise each other. Mayweather is perfect example of this. People actually think the way he acts is for real. He stated nobody wants to see just some mild manner boxer on the verge of a big fight.
Like Ali. Ali biggest influence was a pro wrestler named Gorgouse George, who people loved to hate, and paid money to see him lose. In the end, doesn't matter if they pay to see you lose, the ticket still cost 3.50, or now a couple grand.
Like boxing, there's a face (good guy) and a heel (the guy people love to hate).
Recently there was a fight between Migul Cotto and Sugar Shane Mosley. And before the fight it was impossible to hype it up with those two guys. Cotto has the personality of a robot, and Sugar Shane is as mild mannered as you can get. So during the pre fight interview both just sitting there, relaxed, talking about what an "explosive" fight it's going to be.
That's why a lot people think fights during weigh-in are usually staged, which they likely are, to draw excitment for the fight.