The Rules of the Road state:

Only use a horn to:
(i) warn other road users of on-coming danger, or
(ii) make them aware of your presence for safety reasons when reasonably necessary.

Remember, the horn does not give you the right of way.

Do not use your horn in a built-up area between 23:30 hrs and 07:00 hrs unless there is an emergency

So there we have it. Clear and concise. No way it can be misinterpreted.

A horn should not be used to lambast other road users for mistakes. We all make them, even you Mr/Miss/Mrs Perfect!!
Neither should it be used to beep at learner drivers who stall or are slow moving off at junctions, as happened to a pupil of mine this morning. Here’s what happened:

Sitting at a set of traffic lights, waiting on then turning green. The light changes, immediately my pupil (a 17 year old, on his first real venture on the road) goes to move off and stalls. Within 2 seconds, not 1, not 2 but 3 separate people were blasting their horns. Not mild little beeps, no, full blown blasts of 5 and 6 seconds with only brief pauses for the horn to regain it’s breath. How the young lad held it together to move off properly, after only holding the traffic up for 20 seconds, I’ll never know!!

What did they expect this idiotic behaviour to achieve? Only they can answer.
Ok, I can you are delayed (you must be soooo important). I get that it can be irritating (if you’ve zero patience). I also get that you were probably, maybe still are, a learner (on your 6th provisional) but all that kind of behaviour is likely to do is make the learner (or otherwise nervous fully licensed driver) panic more and therefore delay you further!!

Use your horn in the way it’s designed to be used, not as a display of superiority!!