I think my response would be somewhere in the middle. I probably wouldn't curse the person ("fuck off") but frankly "I disagree, ..." is far too light of a response.

I would ask the offending person to leave. If they refused to leave, I would encourage all of my friends to leave.

Such a statement is so beyond-the-pale inexcusable that simply stating your opposition is insufficient. While I agree you don't need to "go down to their level", I see no reason to allow them any more of my time than is absolutely required (i.e. time spent organizing my friends' departure and paying for the check).