swelled head
swelled head {n.}, {informal}
A feeling that you are very important or more important than you really are.
When John won the race, he got a swelled head.
Pretty girls shouldn't get a swelled head about it.
- swell-headed {adj. phr.}
After he was elected captain of the team, Bob became swell-headed.
Compare: BIG HEAD.
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Source: A Dictionary of American Idioms