"This one is harmless but occasionally can drive someone mad.
My mom has a bunch of framed family photos hangin on a wall. One day I was visiting I took them all down and scanned them with a little hand scanner. I photoshoped small changes on them, removed some people from some photos, added a couple of celebrities in the background, etc, print them out and replaced them a few days later.
I can’t forget her face when she realized it was me and she was not losing it."