if the cap fits, wear it

[Sukie]

Where does this come from and exactly what does it mean?

[Quizmonster]

If A makes a critical remark such as: "Some people are so selfish!" and B replies: "Are you talking about me?"...A might then say: "If the cap fits wear it!" In other words, "If you are selfish, then...yes...I am talking about you!"

It is really a matter of getting someone to condemn himself out of his own mouth.