In my practice, I've seen alot of what I would call "boundary violations". It's not always easy.
A boundary is a line that is created by role, socialization, culture, personal preference etc. We create boundaries in the way that we allow others to treat us and in the way we treat others.
Nurses are physically close and even touch intimate areas of patient's bodies, so often what we do means that our ROLE allows us to invade people's usual boundaries in the name of giving health care (ie cleansing private areas, inserting caths). You wouldn't normally go up to a person and press your body against them BUT we may in essence do that when we pull someone up in bed, help them get up out of bed etc. Most of us will chuckle about, as students, learning to ask people about their bowel pattern because this was so new to us: most of us were socialized NOT to chat about bowel habits UNTIL we went to school. So the role of being a nurse ALLOWS new or different roles in the way you will relate to people who are patients.
Boundary violations, when they occur, are often in the social, emotional and relational realm. Certainly they can be in the physical realm. Boundary violations can include: dating a patient; becoming emotionally attached and coming in early to visit a certain patient repeatedly; becoming so attached to a pediatric patient that you tell a mother that you, more than she, know what's best for her child [seen that one]; engaging in touch for your own gratification; exploiting a patient's trust for your own gain [ie ripping them off for money or things]; becoming triangulated between patient, family, other hospital staff, physicians, etc., gossiping about other patients or nurses and a host of others.
A good self-check about boundary violation is when the behavior you engage in serves YOU more than it serves the patient or client. Another self-check is when you find yourself TOO wrapped up in a client or situation over time. [Most of us will experience a situation that we replay in our heads over and over for a time, but if you're violating boundaries, your putting yourself in direct contact with that patient or person over and over and constantly going above and beyond.]
I would say that most of us find ourselves getting a little wrapped up in things at times, but if it's a pattern or it's an egregious abuse of a patient care situation, it can be career threatening.