Horn

[rotor]

replacing the motorcycle exhaust with one that produces more noise is a sign of social irresponsibility: it is annoying to other road users at all times. A louder horn, used judiciously, is a smart addition to the transportation security.

Seriously - I am surprised by the fact that no motorcycle riding course I've known addressed the topic of smart and judicious horn use. I remember in particular a crash video circulated on the net a couple of years ago, with the left-turning car driver at an intersection hit the bike, where it was obvious the accident would have been easily avoided by one of those 1/10 of a second horn sounds.