The thing in sports, especially fighting sports, is that you need (at least it is highly beneficial) to be able to "turn on the mean" for your performance in the ring/octagon. You have to have ill intentions during the bout. You literally need to treat the other guy like he just raped and killed your family. If instead you go in thinking it is just another day with your buddies in the gym, it just isn't the right mindset.
In a way it is definitely faked, but it is also real. You need to work yourself up to a level of mean. It is an important element of sports psychology -- you need to be there to dominate and intimidate.
The problem with going in with fist bumps, hugs and jokes is that the fight will end up being more like a sparring session and you'll end up fighting for points rather than for KO.
You especially can tell who's good at this based on behavior when a guy connects -- the real pro's like Mike Tyson, Holyfield, Marciano, etc. would jump in for the kill. Wilder has it -- watch how his eyes open up when he gets an opportunity to finish. There's a reason why Mike Tyson said he could tell during the staredown who was going to win, it was about gauging the level of mental dominance.
Anyway, you don't need to make up some sort of soap opera beef outside the ring, but you definitely need to be able to turn on the meanness for the professional encounters.