To be conceited; to have an inflated opinion of oneself.
彼は小さな成功ですぐにうぬぼれてしまう。
He quickly becomes conceited over minor successes.
成功しても決してうぬぼれてはいけない。
Even if you succeed, you must never be conceited.
若い頃は自分の才能をうぬぼれていたと反省している。
He reflects that when he was young he was conceited about his talents.