"I'll know I'm old if I find a photo of myself for sale in an antique store." Making that statement to her sisters was probably not a good thing because one of the sisters stopped by our store one day with a picture of the "victim" and asked if we could help play a little joke. Of course we could! The photo was already framed so we stuck a price tag on it and found a place to put it so that it could easily be seen. The next day the sisters came to the store (there were 3 or 4 of them and they were all in on the joke, except for the victim) and wandered around finding all sorts of fun stuff. We wondered if she would find the photo when a very loud scream made it clear that she had.
About a year later, they were in the store again and told us that they didn't admit to playing the joke on their sister until months afterwards. I'm not sure if the victim ever forgave the others either for playing the joke on her or for waiting so long before they confessed.