Most of my flights include departure and/or arrival from a non-towered airport. A common rub we run into is "runway incursions". An obvious runway incursion is when someone is already on the runway and someone else gets in front of them...that's very obvious. (ie. Someone is departing and someone else crosses in front of them.) The less obvious ones, that lead to the conflict, are the ones where someone comes behind. A common example would be when one plane takes the runway to land or take off and another comes on the runway behind them. Regardless of the fact that calling "line up and wait" is an ATC function, I can't find anywhere in the FAR where this behavior is actually a runway incursion or violation. There definitely is the whole "unsafe manner" clause but, if you're lining up behind a plane that just landed or is departing, waiting for them to clear, the only potentially unsafe thing could be that someone is on final and you're in their way. So, aside from being rude, what is the actual issue with it and when does it actually, definitively, become a runway incursion?