The Laughter Library published 1936 #244

Professor Einstein's secretary was so burdened with inquiries as to the meaning of 'relativity' that the professor decided to help her out. He told her to answer these inquiries as follows: 'When you sit with a nice girl for two hours you think it's only a minute, but when you sit on a hot stove for a minute you think it's two hours. That's relativity.'