As a road cyclist for many years, I've noticed a rather discourteous behavior that some riders are showing when overtaking an unknown rider.
Instead of yelling "On your left" or a greeting, the overtaking rider shouts "Hold your line!"
My guess is that they expect that the stranger will plow through any obstacle that might occur in their path so that he can pass efficiently. In one instance I noticed that the overtaking rider was stretched out on aero bars.
I am probably bothered by this behavior because I don't think the way these people do. If I am overtaking a strange rider I don't assume anything, including that they understand English. I call out "Passing on your left" or "On your left" well in advance, and give them at least two feet of space (usually more). NC law requires that last part. Then I wait until I'm well clear before moving right.
I wonder if these cyclists realize that announcing their presence courteously would get them what they want more effectively? Saying "Passing on your left" makes people aware that they're being overtaken, and most often they straighten up and move further right.
I'm not out to over-generalize this, I've only seen it happen a few times. I would like to avoid having this become the new normal.