1.
vanity, conceit, self-flattery
An excessively high opinion of oneself, especially regarding one's appearance, abilities, or worth.
それは自惚れだよ。
That's just conceit.
自惚れが強い人は周りから嫌われやすい。
People with strong vanity tend to be disliked by those around them.
自分がモテると思っているのは自惚れにすぎない。
Thinking you're popular is nothing but conceit.
RELATED VERB:
自惚れる (to be conceited, to flatter oneself) is the verb form. 自惚れ is the noun derived from it.
USAGE:
Always negative. Used to criticize someone who overestimates themselves. Common patterns include 自惚れが強い (has strong vanity) and 自惚れにすぎない (is nothing but conceit).
WRITING:
The kanji 自惚れ is standard, but hiragana うぬぼれ is also used.