I don't have personal knowledge of this, but from what I can tell, players RARELY hated Lavell. I'm sure there are other coaches on staff that players just couldn't stand, but just about everybody loved Lavell. It was probably Lavell's greatest asset; his ability to be a father-like figure and a friend to everyone he met. Lavell was the glue while his other coaches ran most of the show.
Now, I could see how many more players that have played for Bronco don't like him, but usually it seems like they don't like him because they were unwilling to meet the demands of effort that he has. If you're looking to go to BYU and be coached by Bronco Mendenhall, you're not going to be able to half-yewt it. The interesting thing is that, while players may hate him for being demanding, it's what endears him to the other players who love him... and most love him... again, from what I can tell.
Now, there's one more hate that I think we see a lot more of. It's BYU. BYU... the school. A lot more former and current players hate the school, and the way they and current players were/are scrutinized at times, than any number of players that hated this or that coach... again... from what I can tell.
That separation, to me, is an important one.