A dunderhead is a stupid person — a blunt, slightly comic insult, more at home in an old story or a grouchy joke than in careful speech. It is not a school grade and not a medical word. You say it when someone has done something thick: lost the tickets, walked into the glass door, argued a silly point to the end. It feels a little dated, like blockhead, and that age in the word takes some of the heat out; it can sound almost fond in a family, or merely rude if you aim it at a stranger. Though actually, it does not name a special kind of stupidity. It is just a heavy, thumping way to say the person's head is no help. Kind people keep it for themselves ('I am such a dunderhead') more than for someone who is already hurting.

笨蛋、傻瓜、榆木腦袋（有點老派的罵人話，故事裡比較常見）