Dimwit
Definition 1 of 2

Humor
Using 'dimwit' can add a humorous touch to criticism.

He acted like a dimwit during the meeting.
Insult
Be cautious; 'dimwit' is derogatory and might offend.

Calling someone a dimwit is rarely taken lightly.
Casual
Informal contexts suit this word best; avoid in formal discussions.

He's a dimwit when it comes to math.
Compare with
foolidiotduncesimpletonblockhead
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