Not a genius, just know the difference between your and you're, their, they're and there....
Generally speaking, people
tend to correct another person's grammar, spelling, sentence
construction when they know they're losing or have lost an argument.
Oh and to all the grammar nazis, have yous ever tried typing with a touchscreen?¿?
Grammar is knowing that "Let's eat, Grandpa!" is different than "Let's eat Grandpa!"