The crew over at Vsauce has set out to answer a very important and critical question: would car headlights work at the speed of light? Unsurprisingly, the answer is not simple, but in the process, you do learn a lot about general relativity and photons and other sciencey stuff.
As Vsauce explains, you could never have a car travelling at the speed of light — nothing with mass can travel at the speed of light. So your car would have to be massless; but it would also not experience time, or be able to turn headlights on, for starters.
As with most things involving relativity, it's a little difficult to understand. But if you can follow along for 12 minutes, you'll definitely have some serious knowledge ready for your next dinner party. Just don't invite the physics department. [YouTube]