noun
self-aggrandizement; self-glorification; self-inflation
Refers to the act of making oneself seem larger, more important, or more powerful than reality, often in a psychological or social context. The literal image is of something growing by feeding on itself.
彼の自己肥大ぶりには周囲も呆れている。
People around him are fed up with his self-aggrandizement.
SNSでの自己肥大は、時に人間関係を壊す。
Self-glorification on social media sometimes ruins relationships.
Compound of 自己 (self) and 肥大 (enlargement, swelling). The term is a straightforward Sino-Japanese construction, likely coined in modern Japanese to describe psychological or social self-inflation.