Which word describes acting or done quickly and without thought or care?

The word that best describes acting or done quickly and without thought or care is "impetuous." This term specifically refers to actions that are marked by a sudden or rash decision-making process, typically lacking careful consideration or forethought. Impetuous behavior tends to be spontaneous and driven more by emotion than by reason, which aligns perfectly with the description provided in the question.

While "rash" also reflects a sense of acting without careful consideration, "impetuous" captures the notion of impulsiveness and spontaneity more comprehensively. Other options such as "careful" and "deliberate" directly denote caution and thorough planning, which contradict the idea of acting without thought or care.