For all he knew, those chicks could have been packing weapons. If they were bold enough to come up over the counter that would have been foremost in my mind. That I was about to get cut (at the very least). I'm leaning toward he acted instinctively. I would have grabbed the closest thing to me and started swinging too. And it's not because I'm a 'violent animal' who gets off on hurting people.
They definitely fucked with the wrong person and got their asses handed to them. If not, we could just as easily be reading about a dead or brain damaged Mcy-D's employee.