I took a video camera and a step latter in to my bathroom. I filmed from the ceiling pointing the camera at the toilet and sink for 10 minutes.
That night we were having company over, so when my "victim" went in to the bathroom, I popped the tape in the VCR and told everyone to laugh out loud when "the victim" came out of the bathroom. He came out, and saw us all laughing and looking at the TV. He looked at the TV and saw the toilet he had just used, and was embarrassed thinking we had all just watched him go use the bathroom. We did not tell him the truth until the next day.