This is a true incident, which happened to friends of ours in Grahamstown, South Africa. They invited a Professor to supper. During the course of the evening, it began to pour with rain, the heavens really opened. Because he had walked their, they offered to put him up for the night, to save him having to brave the bad weather. He agreed, and it was settled. While they were doing the dishes after supper, the absent minded professor had disapeared. No one could find him anywhere. Eventually after about 40min, the front door bell rang. There was the professor, drenched to the bone. When he was asked what on earth he had been doing in the rain, he replied that as he was spending the night there, he had popped home to fetch his pajamas and toothbrush.
(From the "Rest" of RHF)