Speaking to both what CheetahGirl and PSYDR have said, I think the evaluation context can be very important here. Also, a thorough records review is always a good idea (when possible).
If, for example, a patient has multiple behavior flags on their chart and has a history of being aggressive toward clinicians, that's likely going to change the expectations I have (for better or worse) going into the first appointment. Likewise, when I worked with criminal forensic patients, my expectations going into the evaluations were different than when I saw students at the university clinic for psychoed evals.
However, I definitely do think there are times and ways in which the clinician's nonverbal (and perhaps overtly verbal) behaviors can exacerbate or defuse some situations. If you initially come across as skeptical, suspicious, or demeaning, you're of course going to potentially pull for "acting out" behaviors from a patient if he/she has a history of exhibiting them. Likewise, if you're going into a session with a patient who has a history of being manipulative (as might be the case with folks with antisocial and/or borderline characteristics), and you present as unsure and lacking confidence, they're potentially going to test some boundaries. But if you present as confident, empathic, and genuinely interested in the patient's well-being (as well as perhaps giving them a few minutes to vent at the beginning of an appointment if they're already very irate for whatever reason), that can go a long way toward fostering rapport.
However, as PSYDR essentially said, if a patient has it in his/her mind to assault you from the outset, there's not a whole lot you can do about it. All you can do is go into every session with a new patient knowing that this might happen, particularly in adversarial contexts.
Edit: As for developing thick skin, it's a natural progression that happens over time. However, no matter how seasoned you are, there will still be specific patients and/or specific things that can be said that will affect you and throw you emotionally "off-center." Being able to recognize when this happens and knowing how you respond is helpful, but hey, we're all human. So if you somehow mess up (assuming it's not some huge ethical transgression like just openly smacking someone), address it afterward as is appropriate and/or refer out when necessary.