Selfish or self-centered; acting only in one's own interest without regard for others.
彼の身勝手な行動がチームの士気を下げた。
His selfish behavior lowered the team's morale.
身勝手な理由で約束を破ってはいけない。
You must not break a promise for selfish reasons.
彼女は自分の身勝手さに気づいて謝罪した。
She realized her selfishness and apologized.