it takes one to know one

1. The person who expressed criticism has similar faults to the person being criticized. This classic retort to an insult dates from the early 1900s. For example, You say she's a terrible cook? It takes one to know one! For a synonym, see pot calling the kettle black. A near equivalent is the proverbial it takes a thief to catch a thief, meaning “no one is better at finding a wrongdoer than another wrongdoer.” First recorded in 1665, it remains current.

Example Sentences

It takes one to know one, of course: Nearly 40 years after Armstrong and bassist Mike Dirnt founded the Bay Area trio in 1987, Green Day is as polished and reliable a rock band as any on the road these days.

From Los Angeles Times

He said it takes one to know one.

From Los Angeles Times

I guess you could say, it takes one to know one.

From Seattle Times

Well, first of all, Dean, it takes one to know one.

From Salon

“These people have done horrible things. They’re criminals. But it takes one to know one.”

From New York Times