We had an elaborate party for an a retiring employee once, and sent out a company wide email with directions to a hotel banquet room, followed by an email to everyone but the employee, telling them to ignore the first email and go to a nearby restaurant instead. The hotel let us put up a couple of signs and some balloons, even though we weren't renting the room. He got there after work and we had three people there to greet him and tell him that nobody else was coming. (His family was in on it. They told him they were busy that night and couldn't come). The three who were there managed to convince him to ditch the "party" and go out to eat with them. They went to the restaurant where over 200 people (including his wife and kids) were waiting. I wasn't there when he got to the fake party, but they taped it, and man, did he look sad! He ended up having a great time at the real party, but when we all saw the tape of his arrival at the fake one, everybody felt bad about the prank.