You say if the shoe fits, wear it, when you are telling someone that unpleasant remarks which 

have been made about them are probably true or fair. It can be slightly rude. The expression is usually used with just the first part of the sentence, as in ‘if the shoe fits…’

Note: The usual British expression is if the cap fits.

For example:

I know you don’t like being called unreliable, 

but if the shoe fits, wear it.

A: “Why do teachers always treat me like some kind of

 troublemaker?” 

B: “If the shoe fits….”

A: “I’m not really a drama queen, am I?” 

B: “Hey, if the shoe fits….“

I have not mentioned any names yet, but I told the team what I think and told them that if the cap fits, they should wear it.

“Are you calling me a liar?” ” Well, I wasn’t, but if the cap fits…”

Tradução: se a carapuça te serve.