General:
* Impulsive: Acting on sudden urges or desires, without considering the consequences.
* Reckless: Showing a lack of care for the consequences of one's actions.
* Rash: Acting quickly and without thinking carefully.
* Careless: Showing a lack of attention to detail or precision.
Negative:
* Blundering: Making clumsy or careless mistakes, often through lack of thought.
* Thoughtless: Lacking consideration or empathy for others.
* Foolhardy: Acting without thinking of the risks or consequences.
* Inconsiderate: Not taking other people's feelings into account.
Informal:
* Blurting: Speaking abruptly and without thinking.
* Spouting off: Speaking in a loud and often boastful way, without thinking carefully about what you say.
* Shooting from the hip: Speaking quickly and impulsively, without considering the consequences.
The best word to use will depend on the specific context and the level of formality you require.