Then there are the folks who do understand the rules but are just plain jerks..
Last week we were sailing almost DDW under light winds on a clear Starboard tack (both by boom position and genoa) and fighting a Maine tidal current. SOG was about 2.7 knots. About 80 yards off our bow, in no danger of a dangerous crossing situation, a sailor crossed our bow on a Port tack. He had over a 1.7 miles of deep water ahead of him on that tack.
Shortly after crossing our bow he tacked over to Starboard. After he tacked over his original point of sail would have had him very, very easily passing to our stern. However, in an arsehole move, to apparently earn a stand on position as the leeward Starbord tack boat, he started falling off, and off, and off, until we were forced to jibe. Once we jibed, and he'd proved his point, he headed upwind again on his original point of sail. This made it quite clear he was just being a jerk..
I hailed him on 16, and he actually answered. I commended him on his understanding of the rules but as a gentleman and fellow sailor I suggested he was acting rather childish with that move. He responded "Rules are rules now aren't they." It was not worth arguing the finer points of the rules and obligations... Suffice it to say his hailing port was not Maine.... Some folks are just a-holes even when out doing something as enjoyable as sailing.