at the drop of a hat
(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.
A rock'n'roll band needs to be able to get under people's skin. You should be able to clear the room at the drop of a hat. Paul Westerberg
I don't believe I ever saw an Oklahoman who wouldn't fight at the drop of a hat - and frequently drop the hat himself. Robert E. Howard
Humans are very aggressive and scrappy, and go to war at the drop of a hat. However, a standard land war is no longer going to work as it is no longer technically possible. Bruce Sterling
There are lots of real men out there - men who could fall in love with you at the drop of a hat. Nicholas Sparks
I'll talk about the Everglades at the drop of a hat. Marjory Stoneman Douglas
Set lists are tough because you come up with this structure of how the songs are going to go from one to the next, but at the same time, you have to be spontaneous and take requests and change the set list at the drop of a hat. Billie Joe Armstrong