迂闊 うかつ
ukatsu

na-Adjective

1. careless; thoughtless; stupid; heedless; unobservant; inadvertent; incautious

Usually Written in Kana
そんな ことをするとはうかつだった。
sonna kotō surutowa ukatsudatta.
It was careless of me to do something like that.
Other forms: