I think that showing some subtle signs of mild frustration can help you show empathy for certain patients, but only in certain situations and with certain patients. If I'm frustrated that a patient is getting EPSE on subtherapeutic doses of antipsychotic, for example, I think that it helps to let the patient know that I am bothered by the fact that they are suffering and that I'm taking it seriously... I've had a lot of patients express that they don't feel like their psychiatrist is cognisant of this fact, which often leads to poor compliance. In other words, if I'm frustrated because I'm empathizing with my patient's frustration, I think that it can help to express that in a subtle way while still maintaining a positive/optimistic outlook.
On the other hand, banging your hand on your head can seem insensitive in many other situations. And yawning is probably always inappropriate.