swollen head
noun [ C usually singular ] uk/ˌswəʊ.lən ˈhed/ us/ˌswoʊ.lən ˈhed/ (US usually also swelled head)
自命不凡，自负，神气活现
If someone has a swollen head, that person thinks they are more intelligent and more important than they really are.
Don't compliment him any more, or he'll get a swollen head. 不要再表扬他了，不然他就找不着北了。
Compare: bighead