I attended one at Georgia Tech and the student section was dressed like missionaries. They thought it was funny. Other BYU fans didn’t like that. It didn’t bother me at all.
I’ve been at other games cheering for the opposing team (nonBYU - MLB to be exact). Yes people gave me stares or harassed me. But I just smile and told them good game. They’re looking to bug me. And I’m not going to let them win by thinking they got me.