numbskull
🇺🇸
/ˈnʌmskʌl/
🇬🇧
/ˈnʌmskʌl/
A person who is not very smart or makes poor decisions.
That numbskull locked his keys in the car again.
その馬鹿はまた鍵を車の中に閉じ込めてしまった。