BECAUSE THEY WEREN'T SUFFICIENTLY EVIL? (profanity alert):

6 Obnoxious Innovations That Will Be in Your Car (Soon) (Dan Seitz Dec 29, 2009, Cracked)

#6. Car Ringtones [...]

How It'll Ruin Your Life:

The "warning sound," as it turns out, isn't going to stop with a fake "vroom." Oh, no, that would be far too limiting in a world where everybody has replaced their cell phone ring with T-Pain. People need to express themselves. So, you'll get cars like the DiMora Natalia, which has an MP3-enabled horn. Yes, the day has arrived when you can toot some Lady GaGa at the guy who just cut you off. [...]

Of course, this needlessly complicates the primary function of the horn: Warning people you're about to kill.