Have passed me to say anything. This happened recently to me a Ute fan walked toward me on the sidewalk and once he had passed me and was a few feet behind me he turned and yelled go Utes.
In that case I believe it is best to pay no attention to it, just act like you didn't hear it, don't turn, don't do anything. Then they get no satisfaction out of talking trash.
Now if they were men about it and said it to your face then a reply would do the trick unfortunately I don't know a good one. I just usually say Utah sucks or something like that.