My 35 years on the roads tells me that in general, Butto is correct. It's oldies, people who lack confidence, knowledge or have an infirmity beneath their poor driving skills. These are also the folk who live in the 20 metres around them rather than the 100+ metres we all know should be a key point in focus. One aberration to this however is that I believe there is an increasing number of aggressive young drivers who do this to taunt other drivers and potentially cause conflict. I have seen the latter more frequently on both the gold coast and sunshine coast highways. One really important point people, please eject any notion of "teaching them a lesson" or "revenge" in your reaction to people who drive slowly in the right lanes. Never forget your primary responsibility is to get yourself (no 1) and other drivers (No 2) to their destination safely and you must do everything within reason to avoid increased risk in these situations. Yes, its human nature to attempt to "sort them out" but this goes against every principle of good driving. It is not your job to discipline such drivers or educate them in real time. By all means toot them to warn of a dangerous situation (totally legal as using the horn is the mechanism to warn of a dangerous situation.....don't go overboard though, if they panic and an accident occurs you maybe held to account), take their plates and report to police or get a passenger to take a photo...all ok. Any legal action to remind them of a dangerous situation is being a good driver. As another poster has said sitting in front of them and slowing down further is merely (potentially) making the situation worse similarly to tailgating.... and may land you in worse trouble yourself. I apologize for the lecturing tone of this post but I'd really like younger drivers to learn to rise above the emotion side of things and think "big picture". It's hard I know, but please consider this when you are in this situation. Remember...it's 90% likely just a poorly skilled or troubled person doing this, not someone trying to play with your mind. Think of them as sick and in denial (hehe)....