They were vulgar, crass and immature at least going back to the late 70s when I went as a kid. They had something ready to go for every team that came in. They have never had a great fanbase, even though they are probably the wealthiest.
USC has a very impressive fanbase compared to other west coast programs. My impressions with them are they are obsessed with the SEC. They also judge their coaches by their ability to beat UCLA. BYU doesn't move the needle for them. I have a few SC booster friends.
UCLA — not much football passion. They support basketball and Olympic sports better relative to football. They really want to beat USC. They do have a longer history with BYU. I attended UCLA, and my impression was most fans respect BYU sports and the older ones will talk about what Devin Durant did or some of the mid 80s football games like it was yesterday. I never heard anyone talk trash about 1984 or religion, but I'm sure it goes on.
The worst fans I have dealt with are those from the old WAC. All of them but Air Force and CSU. I don't want BYU to be in a conference with those schools ever again.