McKean's Law
Formulated by lexicographer Erin McKean, McKean's law states, "Any correction of the speech or writing of others will contain at least one grammatical, spelling, or typographical error."
Darren: You're grammer is so bad.
Tom: It looks like you've become a victim of the affects of McKean's Law.
Tom: It looks like you've become a victim of the affects of McKean's Law.