have a big head

骄傲自大

A: Why does Jane have such a big head today?

B: She got the highest grade on the math test.

Have a big head不是大脑袋，而是指觉得自己很了不起，感觉傲慢。Jane数学考试得了最高分就飘飘然，给同学们的感觉就是have a big head。