Seriously. I used to have the greatest explanation of time dilation using a clock and a space ship and a beam of light, but that's about all I can remember. FUCK.
So this clock, a beam of light, and a space ship walk into a bar. The bartender says... he says.... dammit, he says something pretty funny here... ah... something to do with the drink that the space ship wants... anyways, so the guy on the stool next to them says, "Time dilation? Now I know where I knew you boys from!"