To set one's cap

to make a fool of one.

See also: Cap

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
In a letter criticising her niece Anna's fictional efforts, Jane denounces the phrase vortex of dissipation: "I cannot bear the expression; it is such thorough novelistic slang." Shades of her own Marianne Dashwood (S&S) condemning to set one's cap at as "a most odious expression," "albeit Jane had ventured it in her precocious Lesley Castle.