I avoided a prank once
I've had my share of pranks done to me (yeah, including the image-is-sideways one), but I generally learn from them. One thing I was quick to learn is never leave your PC unlocked in an office - there's always some smart aleck somewhere who thinks he's hilarious.
I was the new guy in an office one day and someone thought he could trick me into leaving the PC unlocked. He gave me a stack of documents to take someplace, shoving them into my arms and telling me it was very urgent.
He thought I was just going to shove off and leave my keyboard to his enjoyment, probably relishing the following admonishing he was hoping to give me about "never leave your PC unattended".
I just reached down with my unoccupied hand and did Win-L, leaving with a smile. Apparently he didn't know that combo.