When he returned home from the Pacific and the Navy some months following the close of World War II, my grandfather began working as a millwright in US Steel's Homestead plant, just outside Pittsburgh. Like many men of his generation, that job would be not only the first of his adult life, but also the last. Late in his career, he was made a foreman in the plant, a considerable promotion, and for a man of his working-class background, without a college education, it was about the maximum height that he could have risen to in his industry at that time.
Near the Homestead plant there was a small bar that catered to the Homestead steelworkers, and pretty much only the Homestead steelworkers. It was the sort of bar where, after a second or third shift on payday, a worker could walk in, grimy and sweaty, and lay his check on the bar. Minus the price of his ten-cent Iron City or Stoney's beer, the bartender would return to the worker in cash the balance of the amount of the paycheck. It was considered a "union" bar, meaning that it welcomed the mill's unionized workers. The managerial and supervisory ranks of the mill, who were not in the union, had their own bar. Socially, the two groups didn't mix after a shift. They went to different bars during the week, different cookouts on the weekends.
After his promotion to foreman, my grandfather was informed that, having joined the "managerial" ranks, it was no longer appropriate for him to visit the union bar after his shifts, as he had been doing for so many years. As family lore tells it, my grandfather had some choice words — words likely learned in the Navy and practiced into a dark art on the floor of the mill — for his new supervisors about their, to him, ridiculous expectation that he suddenly stop socializing with the men that he had worked alongside for so many years. He, dammit (plus a lot of other words), would keep going to his old bar, with his old friends, union or not.
Perhaps less dramatically, the same sorts of divisions continue to govern many aspects of American working life. In the military, off-duty officers and enlisted personnel are prohibited from fraternizing socially. Within the corporate world, the rules are less explicitly stated, and less rigidly enforced, but we all know of the social expectations that make it awkward and perhaps at times even inappropriate for supervisors to socialize too freely with their corporate subordinates outside the workplace. There are frequently subtle, unstated (and sometimes even explicitly stated) social boundaries between the different "ranks" within a corporation. While these boundaries may at times seem arbitrary, or seem to reinforce troubling class distinctions, they do frequently serve a necessary purpose, protecting both workers and their supervisors from both actual and perceived improprieties.
The culture of academe obviously doesn’t map too directly onto industrial, military, or corporate culture. (Although I bet it maps more directly than a lot of us would like to admit that it does.) And yet, we all know — or need to realize — that similar divisions exist within our own professional world. There are unstated but very necessary social boundaries separating undergraduate from graduate students, and separating graduate students from professors. In some university and departmental cultures there may even be a less distinct social boundary within the professorial ranks, particularly between the untenured and the tenured faculty. (Though I would argue that this last division is an entirely unhealthy one, because new professors need to be socialized into the profession by their more savvy and experienced colleagues. Similarly, I think that unnecessary social boundaries between faculty and staff or between tenure-track and non-tenure-track faculty can be quite detrimental to the professional and social health of a department).
In many ways, transitioning from the life of a graduate student to the life of an assistant professor is about learning to cross the boundary between the two groups, hopefully gracefully. Certain parts of university life, like academic conferences, enable a temporary suspension of the boundaries, when graduate students and professors mix more freely outside a classroom or lab setting, and so conferences provide a critical opportunity to graduate students to begin their own social transitions. Conferences, like holiday parties (as we fast approach that season), are often well-lubricated by alcohol, which presents a host of additional social issues that have to be navigated carefully. The role of alcohol (and its perils) in graduate and professorial life probably merits its own column, but suffice to say that everyone needs to navigate carefully around the bottle. Alcohol-fueled behaviors that may go unnoticed around fellow grad students may raise eyebrows among the faculty, and be remembered. Similarly, a faculty member, for example, whose lowered inhibitions led them to rant against a colleague in front of students would clearly be acting unprofessionally.
Management’s expectation for my grandfather so many years ago was that he could remain friendly with his old crew, but that his new position necessitated a new set of friends. That was almost certainly a ridiculous expectation under the circumstances, but navigating social expectations and boundaries is important to leading a successful career in academe. But because those of us in academe often like to think that we’re more egalitarian and open-minded than others, acknowledging that there are certain necessary social boundaries within our professional lives is almost taboo. And because we don't acknowledge such boundaries as openly as we might, they become even harder to navigate.
These social boundaries between different constituencies within academe, while they do exist, are troublesome within the academy, because many academics don’t see our world as one governed by the same sorts of social conventions that typically govern corporate life. That fuzziness can lead aspiring or newly minted professors astray when it comes to matters of propriety and decorum. For example, very young graduate students may sometimes identify more with undergraduates than with their graduate student peers. Much more commonly though, young assistant professors, just months removed from their own graduate studies and often separated by many years of life and professional experience from their professorial peers, often identify closely with the graduate students at their new universities.
The differences between undergraduates, graduate students, and the professorial ranks are relatively easy to identify. When you are a graduate student you shouldn't and can't go to the party that an undergrad invites you to. When you're an assistant professor, you shouldn't hang out with your grad students at the bar every week, but it might be perfectly appropriate to (as was done for me and as I continue to do for my own grad students) buy them all a round at the end of the semester. After those divisions though, the social boundaries that govern university life become much less clear, and begin to vary dramatically from institution to institution.
Among other reasons, social boundaries are part of why programs don’t hire their own graduates — a grad student hired into the professorial ranks of his or her own program would forever remain a grad student in the eyes of fellow faculty, and until there was a complete turnover in grad students (which could take a decade) would live in an uncomfortable social limbo between graduate student and professor. And every faculty member you know probably has a tale about assistant professors who made a perfect ass of themselves by slapping their new dean on the back at a reception, or by partying with the grad students. Don’t be that assistant professor.
It's my own opinion that beginning assistant professors (hell, all professors) should be friendly with everyone they encounter in the workplace (undergraduates, grad students, departmental staff,  fellow professors, administrators, everybody else), but that they should be careful to maintain conventional social boundaries. The exact placement of these boundaries is likely to vary from institution to institution, and so part of your job as a beginning assistant professor will be to observe carefully, in order to figure out the expectations that your fellow faculty have for you, and the norms of acceptable socializing and behavior in your new department. If those boundaries seem unhealthy or unfair, you may be at an institution that isn’t quite right for you, but don’t, as my grandfather did, cuss out your colleagues. He got away with it, but you probably won’t.