I do this a lot. Don't most people? If someone randomly laughs, I assume they're laughing at my animal hat, homemade spectacles, or derpy face. :) Or they just had a funny thought like most folks ought to. Maybe a funny memory, or a funny plan for the future. If someone asks me while I'm laughing, I'll usually be honest and tell them in detail. They often regret asking.
“You have evolved from worm to man, but much within you is still worm. Once you were apes, yet even now man is more of an ape than any of the apes.” -- Friedrich Nietzsche
"The universe is random. Not inevitable. It's simple chaos." -- Walter White
"Of course it is happening inside your head, but why on earth should that mean that it is not real?" -- Albus Dumbledore