(it) takes one to know one

(it) takes one to know one

A childish retort used to suggest that the person who has accused someone of being some negative thing is in fact that thing (as if being that thing would help one to identify others of like kind). A: "You're a real jerk!" B: "Yeah, well, it takes one to know one!" A: "I don't want to sit next to her—she's a nerd!" B: "Takes one to know one!"
See also: know, one, take
Farlex Dictionary of Idioms.

(It) takes one to know one.

Inf. You are one also. A: You are a stupid oaf. B: So are you. It takes one to know one.
See also: know, one, take
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

it takes one to know one

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.
See also: know, one, take
The American Heritage® Dictionary of Idioms by Christine Ammer.

it ˌtakes one to ˈknow one

(informal, disapproving) you are the same kind of person as the person you are criticizing: ‘Your brother is a real idiot.’ ‘Well, it takes one to know one.’
See also: know, one, take
Farlex Partner Idioms Dictionary

it takes one to know one

The critic is as bad as the person being criticized. This expression, a modern version of the proverbial “set a thief to catch a thief,” and “a thief knows a thief as well as a wolf knows a wolf,” dates from the early twentieth century.
See also: know, one, take
The Dictionary of Clichés by Christine Ammer
See also:
  • it takes one to know one
  • takes one to know one
  • tell me about it
  • the genuine article
  • genuine
  • genuine article
  • far be it from (one) to (do something)
  • far be it from me
  • far be it from me to
  • far be it from one to