My Thoughts on This 
1. It irks me when people don't dress properly when they go somewhere. I remember being a little girl and putting on my sunday best for a plane trip and now people fly looking just like they rolled out of bed onto the airplane. I can't cite them, but I know studies have been done that show people "behave" better when they are dressed in a less casual manner.
2. I can't imagine my daughters behaving like that in a restaurant and they are 5 and 7. They're not perfect, but they have been taught to behave when they're out in public. Obviously, those girls in the restaurant are lacking a proper role model.
3. I was always taught that it is poor manners for a man to wear a hat of any kind (except something with religious connotations like a yarmulke) indoors. Do these folks think they're Garth Brooks or something?
4. I also normally enjoy watching people make fools of themselves! However, if I am paying $100 for a nice, quiet dinner in a good restaurant, I prefer a more peaceful atmosphere.