Get rickroll and copy then rename/resize it (cut off the end, or add silent padding if necessary) so that the song length and name is exactly the same as the victim's mp3 playlist. Double points if you can make the change easily done and easily revertible. Triple points if you can make a virus that re-pranks the person automatically after a month (but only if its revertible of course). Also, how many people here have thought of doing something like this? I'm guessing 90%.