Are you saying it was ok for Buzz to return the favor to the student section, regardless of whether or not it was professional of him to do so? In your estimation, it is ok to yell expletives at someone while you are on the job, even knowing fully well that it is a part of the job?
If that is not what you're getting at, please correct me because I am just misinterpreting it, but if that is what you're saying, allow me to provide an example of why this is not acceptable.
I teach in the inner city. I hear expletives all day every day, and occasionally they are even directed toward me. That is fine, I realize that is a part of the job - if I'm not able to accept that, then I shouldn't be working in the position I do. In no way will it ever be acceptable for me to use profanity toward a student, even if they use it toward me first. I will lose my job within 5 minutes if I do that.
Similarly, think about customer service representatives, telemarketers, credit collectors, etc. I'm sure they hear rudeness and profanity all the time, but they know it is part of the job, so they do not treat customers in the same way they are treated by the customers. If they do, they also will lose their jobs.
In general, you are correct - no one should be surprised if they yell expletives at someone and the sentiments are returned. However, if someone takes a job knowing full well that being mocked and cursed at is part of the deal, they shouldn't be returning those sentiments.