Similar to saying "look who's talking!"; a
comeback for when
somebody says or insults
something or somebody, but the statement is hypocritical
Clark - "Hey
Neil! You're so stupid!"
Neil - "Says you! You're the one with an F in Math!"
Bob - "
Wow! This paragraph is the mos sloppy thing I have seen!"
Mark - "Says you! All you wrote about was how 2+2 is equal to 5!"