Thats all just speculation, cant be cerified. Being hard to get along with is a trait a lot of football coaches have and in some cases, it's a good thing. I doubt his players hated him when he won a Super Bowl.
With a little hunting, you can 'certify' a number of these things. I'm sure Keyshawn would be happy to tell lots more, if they weren't both working booths. Again, even his friends comment on his issues.
http://fifthdown.blogs.nytimes.com/2009/01/17/jon-gruden-is-the-larry-brown-of-the-nfl/?_r=0
"He can never love his players — especially his quarterback. Jon always wants new, even when new is not necessarily better. He was instrumental in returning the Raiders to their glory days with the help of some key players, notably Rich Gannon, then went off to Tampa to have all the power and ability to run his own show. That’s where his downfall started.
Jon’s inability to truly “Love You, Bro” prevents him from being successful. He does not want to fall in love with any one player, and he is very hard on the players.
I once referred to Gruden as the Larry Brown of the NFL. I meant that as a compliment because I love Brown, but when Brown, the well-traveled NBA coach, has control of the personnel on a team, he makes horrible decisions and hates the players he coaches. He wants new, but after new is over, he wants more new. Does that sound familiar?
After the firing, receiver Michael Clayton was quoted as saying: “How do you build a championship team with all the inconsistency? You have to do it the right way. I’ve always been a person who feels like you reap what you sow. You have to treat people fairly.
“It’s about showing more confidence in your players. He was kind of a turncoat. He’d tell you one thing and then do something else.” "