There is nothing wrong with a bit of healthy ego especially in sport or when down the pub with your mates having a drink. It helps with getting things done and can be entertaining. I suppose like everything though there is a fine line between having enough self confidence and belief in yourself to get the best possible outcome and too much belief and ego that things go terribly wrong.
I used to see it all the time when I was coaching and helping with junior sport. We would encourage the team to be loud, confidant and take a risk, it would bring the best out of them and also teach them a bit of humility when it did not work and we looked silly.
Some of the parents of our players and opposition thought I used to have a big ego but as a coach I was just doing my job.
I don't think I have ever had a problem with it myself, I am more of an introvert but I do remember playing in this grand final once a long time ago with my local football team. It was only a low level evening competition after work but boy did they take it seriously. The Egos were massive on both sides all over the ground. There was constant niggling and wrestling, send offs and arguing with the umpire. I had not seen anything like it before. The referees warned both sides to cool it down but just before half time the ref blew his whistle again and called the match off, with not result recorded. Too many big egos ruined everything for everyone.