At the VA, I did a rectal on every patient that consented. First of all, several of them had some degree of urinary difficulty, which warrants a prostate exam. As for others, I didnt tell them that I "needed" to do it, but I told them being a male over 50, theyre at increased risk for prostate cancer, which is true. I told them that one way to screen for prostate cancer is by digital rectal exam and if they would like to be screened, I would be willing to do it. Most agreed and the ones that did not, I respected their decision and never brought it up again.
Youre just dissing the rectal exam because of the stigma of the test itself. If someone comes in with nausea and diarrhea, you still do a good cardiovascular and respiratory and neuro exam, although most likely they just have simple gastroenteritis. You are probably not going to find any significant findings in many other body systems, but you do it anyways. Regardless of whether you absolutely need to do it or not, you should be practicing your clinical skills as much as possible as a third year. As long as they consent and your being honest with them, there is nothing wrong with doing things that are a bit uncomfortable. I imagine that you would have no problem drawing an arterial blood gas from a patient when there are more experienced people around you could potentially put the patient in more pain and discomfort than someone more experienced.