General synonyms:
* Foolish
* Ill-advised
* Rash
* Imprudent
* Unintelligent
* Stupid
* Careless
* Thoughtless
* Indiscreet
More specific words:
* Naive: Lacking experience, wisdom, or judgment.
* Shortsighted: Failing to consider the long-term consequences.
* Reckless: Showing a lack of care for danger or consequences.
* Impetuous: Acting quickly and without thinking.
* Headstrong: Stubbornly determined to have one's own way.
* Oblivious: Unaware of or not paying attention to something.
* Deluded: Holding false beliefs or ideas.
* Misguided: Having wrong or mistaken ideas or goals.
The best word to use will depend on the specific context. Consider what you want to emphasize about the person or action being described as "unwise."