Does it really "take one to know one?"

[T'Baio]

My fiancee' works with developmentally disabled children.

We've come to be quite close with one kid, he's really cute.

Anyway, even developmentally kids can be cruel to each other, and they hear insults from the world that they occasionally use on each other. The other day, one kid called another "retard," to which that kid responded; "takes one to know one."

I'm now worried about my mental acuity.

 

[Velocity]

It doesn't always "take one to know one", but one often does recognize another one.

 

[Mr. B]

The kid who was being taunted actually sounds pretty smart.