Change your horn sound! Actually, I always thought it would be nice if there was also a "friendly" horn - something that you could press to indicate "hey, you left your signal on" or such without inspiring the instinctive annoyance that regular horns do.
Appropriate warning-of-impending-crash songs: Mazzy Star's "Fade Into You", R.E.M.'s "Bang and Blame".
Inappropriate horn songs: Mousse T vs Hot 'n' Juicy "Horny".
(via the MIT Advertising Lab)