at the drop of a hat

at the drop of a hat  {adv. phr.},  {informal}
1. Without waiting; immediately; promptly.
If you need a babysitter quickly, call Mary, because she can come at the drop of a hat.
2. Whenever you have a chance; with very little cause or urging.
At the drop of a hat, he would tell the story of the canal he wanted to build.
He was quarrelsome and ready to fight at the drop of a hat.
Categories: {adv. phr.} {informal}