I mean, context is everything. Whether "dickhead" is unacceptable really depends on the culture of the workplace communication. If the response to someone calling you a "dickhead" is that you tell them twice to "fuck off", you're going to have a hard time making the argument that your workplace communication is expected to be explitive-free. And, "I only stayed here because of you two dickheads" is hardly toxic -- it's elegantly (by certain metrics) communicating an anguished sense of personal loyalty betrayed.

In another context, where "dickhead" was really out of place in the expected communication culture, and where it was really meant to be toxic rather than used to expressed an anguished sense of betrayed loyalty, "Mrs. Jones, I'm afraid I'm going to have to ask you to leave the building. The personal effects from your desk can be collected from reception tomorrow" might be more tolerated.