An informal, slightly teasing name for someone who is very clever with books and ideas, and who seems to live in thought more than in everyday jobs. People who say it often mean “you know a lot — but maybe you are not practical, and maybe you think you are smarter than us.” It can be a joke between friends, or a real put-down. It is more American than British, and it feels a bit old now; younger people more often say nerd or geek, which are close but not the same. You would not write it as praise on a school report. The pieces are just egg + head. People often picture a round head, like an egg, but that is the joke in the picture, not a second meaning of the word.

蛋頭、書呆子（帶點調侃，不是在誇人）