people in the rivalry jokingly said, "oh I hate that shirt" when someone is wearing a rival shirt? It happens every day in life and it's very rarely meant to be starting a fight. If someone takes offense to a "hate that shirt" jab, they are taking the rivalry WAY too seriously.
If a waiter said he hated my hat or shirt because he was a Utah fan, I'd laugh with him and make some comment back about his team because I'm an adult and don't take offense to "I hate that shirt" comments.
I see almost no possibility that the waiter in this story was meaning to be confrontational. I've just seen too many "I hate that shirt" moments in rivalry banter.