I mean everyone's figured this out more or less though.
Gentle horn tap - polite, informative. "The light is green and you're spaced out, mate".
Pronounced depression (or two) on the horn - stern, informative. "You just swerved into another lane without indicating in heavy traffic, your behavior is risky".
Long extended honks, wild honking, something resembling Morse Code - impolite, abusive. "You just blew a stop sign", "you're driving on the wrong side of the road". "You could kill someone you fucking arsehat".

