Headlight fluid is the same running joke as blinker fluid. But instead of specialized for your turn signals, with its orangey color, headlights fluids are supposed to be whitish or yellowish in tone. The premise is the same... Your headlights are flooded by rainwater or moisture leaking in. But, to someone who might not know about cars, they might think that your headlights are instead leaking their headlight fluids out. So, they should probably head out and buy a bottle of headlight fluid. They have these gag items for sale on Amazon and elsewhere, too.