When me and me friends went to Germany with the school (we live in the UK) we were staying on the bottom floor . We were getting ready to go in to the village and my friend who had been pulling pranks on us all through the trip was in the shower so the rest of us went outside and told every one to come stand in our room. We then took the towels from the bathroom. We shouted goodbye and pretended to leave the room. A few minutes later he came out the shower and shouted for a towel. We stayed quiet so he thought we were out of the room. He came out of the bathroom naked where we stood with cameras and about 30 other people. He freaked out and had to stay in another room on the floor for the rest of the week.
(Source: College Humor)