Utah State was the worst, but it never got any worse than comments about wishing we weren't sitting in the season ticket section (seats were my uncle's). When an usher came to move some folks who were sitting in our row, but were in the wrong section a number of fans pointed and yelled at us hoping they would move us, but they didn't and that was as bad as it got.
Notre Dame, Wisconsin, Mississippi and AFA were all pretty gracious hosts and I don't remember any incidents at UNLV either.

For basketball, my experience has been a little different. I did not enjoy my experience attending the MWC basketball tournament at T&M because of the obnoxious commentary from UNLV fans. This experience, combined with others, with UNLV fans (in Provo or on the road) at basketball games has left me unimpressed. There were also a handful of Utah fans around us that had a little too much to drink and weren't very fun to be around, but I choose not to generalize about Utah fans based on this small sample. Wisconsin fans were fine (game was in Chicago and we got beat) and the MWC fans were fine when the tournament was held at the Pepsi Center years ago as well.

I have only ever been to one road volleyball game and it was the National Championship tournament this year in Chicago. Everyone was nice and the reality is that many of the people in attendance really didn't know much about BYU (except for those there supporting Stanford).