If you were fired because you would not follow directions of a supervisor or if you were disruptive, you can argue that your working environment was very casual.  Tell your interviewer that you have even heard swear words and name calling within the environment and that your actions were normally tolerated. If you can remember any times that you exhibited the same behavior and were not reprimanded, state those times as well.  You are proving that you had no idea you would get fired over something that is generally accepted by your co workers and your management staff.

If your comments were not vulgar or obscene argue that point to your employer.  If there was a person who started the whole incident and you were just responding to what they said, that information is key to your defense.  Tell them about the other person’s outburst and that you tried to keep from getting into the middle of it but the person kept at you until you had defend yourself.