BMW revealed that it had developed a new "Toot and Calm Horn" (T.C.H.) system, which made a noise that actually calmed other drivers on the road rather than aggravating them, thereby lessening the risk of road rage. The name "Toot and Calm Horn" was styled after Tutankhamen.
This April Fool ad has been fairly widely reported, but I don't know where or when it ran. The earliest report of it I've found dates to 2006. I'm guessing the ad may have run in the 1990s.