half-cocked

Prematurely. Like “flash in the pan,” “half-cocked” is a phrase that comes from old firearms. The firing mechanism of a flintlock pistol or musket could be set at full cock, or ready to be discharged, or half cock, which was the equivalent of having a safety on a revolver. A weapon that went off while half-cocked did so prematurely, just like someone who loses his temper without considering the facts or consequences of a situation. To act too soon, especially in a rash or impetuous fashion, is to go off half-cocked.