big head指一个人过于自负，爱吹牛，自命不凡。

【例句】
I'm getting tired of Gerald telling us how he won his school's sports cup; he's becoming a big head.
我变得讨厌杰拉尔德了，他老是对我们说他是如何赢得学校运动会奖杯的。他变得爱吹牛了。

We didn't tell him because we didn't want him to get a big head.
我们没告诉他是因为我们不想他太骄傲。