This was at a small event that we ran some years ago. The party is walking along a path which bends around a slope into a gatehouse. The leader sends one of the group on ahead to scout. In the archway of the gatehouse he discovers a large phys. He trots back to the main group.
Party comes round corner, into clearing.
They discover a Ford Transit, covered in a dressed tarpaulin, with a large head bolted on the front. We had built a dragon. The party was being led by the hardest character in the system. I think the silliest thing that ever happened to me in a game happened during a module that was being run on a Sunday in May. My son was with one of the groups that was going through that day.