Thinking too well of yourself — believing you are more important, more talented or cleverer than you actually are, and showing it. The picture behind the word is a head that has swollen up with pride until it is too big.

Thinking too well of yourself把自己想得太好 believing you are more important, more talented or cleverer than you actually are相信自己比實際上更重要、更有才華，或更聰明 and showing it而且表現出來。 The picture behind the word這個字背後的畫面 is a head that has swollen up with pride until it is too big是一顆因為驕傲而腫得太大的頭。

It is informal, mildly insulting, and slightly old-fashioned; it is mostly American, and it often turns up when success has gone to someone's head: a young player who wins a few games and starts ignoring his teammates. It carries a hint that the person did not use to be like this, which is why it stings — you are saying they changed for the worse.

It is informal, mildly insulting, and slightly old-fashioned這是非正式、帶點侮辱、也有點過時的說法 it is mostly American主要是美式用語 and it often turns up when success has gone to someone's head常常在一個人「得意忘形」時出現 a young player who wins a few games and starts ignoring his teammates例如一個年輕球員贏了幾場比賽後開始不理隊友。 It carries a hint that the person did not use to be like this它暗示這個人以前不是這樣的 which is why it stings這也是為什麼這個詞會刺人 you are saying they changed for the worse因為你等於是在說他變得更糟了。

It is also written swellheaded or swell headed, and Britain has the same idea as big-headed. The related expression 'it went to his head' says the same thing without naming anyone rude.

It is also written swellheaded or swell headed也可以寫成swellheaded或swell headed and Britain has the same idea as big-headed英式用法則用big-headed表達同樣的意思。 The related expression 'it went to his head'相關的說法「it went to his head」 says the same thing without naming anyone rude表達同樣的意思，但不會顯得沒禮貌。

Note that swell here is the verb meaning to get bigger, not the older American slang swell meaning excellent.

Note that swell here is the verb meaning to get bigger要注意這裡的swell是「變大」這個動詞的意思 not the older American slang swell meaning excellent不是舊式美式俚語裡表示「很棒」的那個swell。