Isn't this a little like the play in football where one player lands a cheap shot on another and the second retaliates? The ref sees the second and calls the penalty on him.
My question is, what did the FTA say/do to provoke the comment? You can't tell me that the person that was doing the yelling was yelling just to yell. Obviously he/she disagreed with whatever was being told to them. Was their reaction appropriate? Maybe/maybe not. Did they go back after cooling down and apologize for their behavior? We don't know. The bottom line is we just don't know without knowing the full situation.
People are people and can get fired up in the heat of the moment. Sometimes they take it too far. This is life. Anybody that comes here and claims to have never said something that was inappropriate or that they regretted later is just flat out lying.
Just to lighten the mood a bit....what if that person's grandmother swore like a trucker and that them standing up for themselves made her proud....would that fall into the GP category?
