I know you are but what am I?

I know you are but what am I?

A childish, teasing response to an insult. A: "Monkey brain!" B: "I know you are but what am I?"
See also: but, know, what
Farlex Dictionary of Idioms.
See also:
  • be not to know
  • before you know where you are
  • as you know
  • as we know it
  • know (something) in (one's) bones
  • I know
  • know where it’s at
  • by any chance
  • AFAIK
  • closed book, a