rash, hasty, impulsive

(しょうどうてきに) This doesn’t always have a bad meaning. If you are walking down the street and impulsively decide to walk into a store to buy a cup of coffee, you can use this. But usually it’s used about kids, who behave impulsively, without thinking of the consequences of their actions.   $$$
(けいそつ) This is the word for the rash cop in a buddy-cop movie:a guy who goes off half-cocked, who is too aggressive, and easily baited.  Although in real life, 軽率 behavior almost always leads to failure.
(むぼう) Unlike the others, 無謀 decisions are made with full knowledge of the consequences. 無謀 is less like ‘rash’ and more like ‘drastic.’
(むちゃ) Can be used to mean rash, but usually means reckless or extreme.  The fellows from Jackass, for instance.  Doing things that one knows are dangerous.