呆
呆 – Dai1 – Foolish, Stupid
You can describe someone as 呆呆的 – Dai1 Dai1 De5. This means stupid in a sort of naive and airheaded, almost cute way. 奔 – Ben1 means just regular plain old stupid.
Another expression is 發呆 – Fa1 Dai1 – Give Out Stupid. It means being dazed, or daydreaming, just standing there and staring off into the distance and being stupid. Yvonne saw a squirrel totally 發呆ing out at the new house today, it was staring at this tree when they got there, and standing in exactly the same place staring at the same tree when they left.