間抜 まぬ
manuke

Noun
na-Adjective

1. stupid; foolish; idiotic; inane

あいつはクラスでいちばんのまぬけだ。
aitsuwa kurasude ichibanno manukeda.
He is the dumbest kid in the class.
Noun

2. fool; idiot; blockhead; half-wit