What are you doing?!?
You want to go with slightly condescending, like you are giving the person the benefit of assuming they will recognize their behavior is ridiculous or dumb if you just point it out, and they just didn't realize yet because they got wrapped up in their mind with the nonsense.
For example: What are you doing? While motioning vaguely at the Huskers.
So asking it to fuck off is the best we can hope for.