The following clip was from a film called "Brotherhood", where a Yankee fan walks into a bar and confronts two Red Sox fans. They tell him to take off his shirt and it escalates from there. He finally goes over the line at the end and pays the price.
Beware, lots of colorful language in this clip. BTW, notice the shirt the Yankee fan is wearing has no New York logo on it. The film's producers would have had to pay rights fees had the guy worn a "legitimate" Yankee shirt. It just has a very small "New York" on the front corner of the it.
With thanks to Fenway Faithful for alerting me to the clip.