at the drop of a hat

From the customary starting of competitions by making a sweeping downward motion with a cap.

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at the drop of a hat

1. (informal, idiomatic) Without any hesitation; instantly.

   Synonyms: at a moment's notice, at once, in a heartbeat

   We're expected to just do it at the drop of a hat.

   If you need help, just call on Mike. He can come at the drop of a hat.

   • 1957, Jack Kerouac, chapter 1, in On the Road, Viking Press, →OCLC, part 1:

     A tremendous thing happened when Dean met Carlo Marx. Two keen minds that they are, they took to each other at the drop of a hat.

   • 2014, Becky Rutledge, Miss Becky's Charm School‎^[1], Citadel Press, →ISBN:

     Let's face it. We are swollen up like an overfed slug, our breath stinks, the tiniest irritant is magnified ten thousand times, and we cry at the drop of a hat.