This reminds me of a story.
One of the best pranks I've ever pulled on my friend.
He bought a macbook and had it for a while. I was using it one day and found porn on his computer. I went into the start up items in the prefs and selected all the quicktime porn vidoes. So every time he turned on/logged into his computer all of the movie popped up.
It took him ages to figure out how to undo what i did.
that's so funny but mean especially if he turns his computer on in public. I bet his uptime isn't that long or prays for a software update