not the sharpest tool in the box/shed (also not the brightest crayon in the box), not the brightest bulb on the Christmas tree informal used to say that someone is not very intelligent or is not able to learn things quickly or easily – used humorously 〔某人〕并不是很聪明，学东西并不快〔幽默用法〕 → not the sharpest tool in the box/shed at not(5)