There will always be a gray area in definitions needed to try to divide "unacceptable" behavior from "acceptable" behavior. It's much like trying to make a universally accepted definition of curse words or pornography. Each person will have their own personal yardstick that they use to measure such concepts. And it's highly unlikely that everyone will agree on any one definition chosen.
In this instance, the use of personally derogatory slurs in what should be a professional discussion is the issue. For instance, calling someone a "son of a bitch", is really not a professional assessment and refers to something of a personal nature that the caller probably cannot prove. Such terminology has only one likely desired outcome, and that is a blatant attempt to inflame the situation and knock the thread completely off the track of being a professional discourse about business ethics and procedures. This, of course, detracts from the discussion, and pulls the discussion further from the goal of actually reaching some resolution between the affected parties. It is more an expression of an emotional assessment of the situation rather than a logical and professional assessment. It also reflects poorly on all the participants engaged in the conversation, because let's face it, once the discussion goes that route, no one is going to actually remember who it was that pushed the discussion into a mud slinging affair, they will only see the results and pretty much believe that everyone is partaking in that sort of garbage. Quite likely they could simply discount the entire conversation as being nothing more than pure garbage being spouted by all participants. It also reflects poorly on this site by allowing it to take place without efforts being expended to throttle back the invective.
As for painting black and white rules about what exactly is acceptable and what is not, sorry, that just is not possible to do. So many terms and phrases can mean different things based on the context they are used in, that to try to make exact examples would be pure folly. Hell, I remember one member thinking they could bypass the rules on profanity by quoting a passage in Portuguese.
If you draw a defined line in the sand, some people will try to see how much of their toe they can put over it.
The best advice I can offer is to use common sense about how and what you post. If you would be offended being on the receiving end of what you are about to post, then reflect on the wisdom of clicking that Submit Reply button. Is what you are about to post going to help make things better, or make things worse for everyone involved in that discussion? Is what you are about to post going to be something you would be comfortable with hearing a prosecuting attorney asking you in court what exactly you meant by that statement in the pursuance of a libel lawsuit?
Think about the reactions to your actions.