I-know-you-are-but-what-am-i definitions

(rhetorical question, colloquial, childish) Assertion that an insult made by the party to whom the phrase is directed is actually true of that party, and not of the person using the phrase. Usually considered to be a playground taunt.

Origin of i-know-you-are-but-what-am-i

Uncertain, but dates back at least to the 1970s, as reported in Lee Thayer, Communication (1974), p. 21.