See also: check yo self before you wreck yo self
Isaac: "Whatever. Your math skills are mediocre at best. I bet you couldn't even prove the Pythagorean theorem with a compass and a straightedge."
Phineas: "I believe those are fighting words. Let's take this outside. I'm going to slap you silly with my pocket protector!"
Isaac: "I suggest you check yo self before you wreck yo self. I've got three of my chess club buddies backing me up and one of them takes taekwondo!"
Variations of this phrase, such as "Check yo self foo!" and "Check yo self before ya wreck yo self" are also used to communicate the same message: correct your behaviour (idiot/before you get in trouble)