As I said before, someone riding my wheel doesn't bother me. It does bother some people. I ride several bike lengths back on riders that I come up upon if I have no intention of passing. Some riders care, some riders don't care. In my experience, it has nothing to do with their level of expertise. I find, in many cases it has more to do with how tired they are. Riders seem to be grumpy at the end of a ride and little things seem to bother them more.