Muphry's Law, McKean's Law, Hartman's Law: You're totally going to have a spelling or grammar mistake in that thing you wrote attacking someone for their grammar or spelling.
It's true facts, and I think it's great. I say, why not put your own error in their somewhere so at least you know where it is? Like being the first person to scratch the paint on your new car.
It happens to Seth Myers in a bigger-than-usual way in this clip around 0:56. Enjoy!