Your attending will have ways of spotting good (or poor) interpersonal skills with patients. It's inevitable that the attending is going to ask a patient about past medical history or current symptoms in such a way that s/he will get a totally different response from the one you got - even if you have good communication skills. But if you have crappy interpersonal skills it's going to happen MORE of the time and the attending can smell the bull$hit.
Also, attendings (at least in some rotations) will see these patients later. They'll see them in follow up in their offices for example, or they'll stop by on their way out of the hospital in the afternoon, when you are NOT there. Don't you think they hear about the stupid medical student or the uncaring resident? Oh, yes, they definitely do. And they don't like it.
Attendings were students once. They learned all the same shortcuts and they had the same guilty feelings about pulling stuff out of their a$$ that many of us experienced in med school. They had the experience of saying, "Mrs. Jones states that her chest pain started when she was sitting in her chair," only to have Mrs. Jones tell their attending when he asked, "Why, yes, doctor, I had been gardening all morning and had just climbed two flights of stairs." Don't go trying to suck up to attendings. Just do your job, do a good job of it, and you'll be okay.
As someone else said, the best way to look sincere is to BE sincere. Be decent to everyone. Treat people the way you'd want to be treated. Talk to them the way you'd want someone to talk to you, or to your grandma. Third year isn't some game where you're trying to get the highest score. It's about establishing the fundamental clinical skills that will enable you to be a good doctor. Sheesh.
