Any radio commercial that has a car horn beep.
It may just be me (I am sure you'll let me know), but I can't tell you how many times I have been startled by a radio commercial 'horn' resulting in me looking around quickly to see who in the world is beeping at me. Of course, I quickly realize it's the darn radio, but it bothers me.
But then again, most folks are probably sharper than me.