Have any of you ever pulled "musical pranks" on your friends?

I've done this on two occassions. The first time was when I put the
song "Sugar, Sugar" by The Archies in the middle of a metal-playlist
my friends and I were listening to on the way to a concert downtown
(the radio I got for my birthday lets me hook my iPod up to it).
Another time, I was doing the same thing and I put the song
"September" by Earth, Wind and Fire in there (not in the same exact
spot though).

What are some musical pranks you have done, and what are some other
music-related pranks I should do?