It is slightly embarrassing to be one of the handful of old people in the MUSS but I love going to games with my kids and their spouses. We have a lot of fun. I have heard exactly ZERO anti-mormon comments in 4 years of going to every game. I did hear someone try to start a group FU BYU chant and I told him to shut up. The same guy had started an FU TCU chant earlier in the season and I didn't want to hear it. I am surrounded by mormons in the MUSS - that might be part of the reason I don't hear anti-mormon comments.
I did hear anti-mormon comments during BYU games when I sat in a different section. There was a group of stereotypical tailgating drunk fans about 10 rows in front of us. There were no anti-mormon comments in my nearby vicinity because we were all active mormons.