Calvin and Hobbes by Bill Watterson for April 13, 1990
Calvin: Dad, will you explain the theory of relativity to me? I don't understand why time goes slower at great speed. Dad: It's because you keep changing time zones. See, if you fly to California, you gain three hours on a five-hour flight, right? So if you go at the speed of light, you gain more time. Because it doesn't take as long to get there. Of course, the theory of relativity only works if you're going west. Calvin: Gee, that's not what mom said at all! She must be totally off her rocker. Dad: Well, we men are better at abstract reasoning. Go tell her that.