na-adjective, noun
self-willed; doing things to suit one's own convenience
Describes a person who acts or speaks in a way that prioritizes their own convenience or desires, often without regard for others. Commonly used as a な-adjective or noun.
彼の得手勝手な態度にはもう我慢できない。
I can't stand his self-willed attitude anymore.
得手勝手に振る
If you act only to suit your own convenience, you'll lose the trust of those around you.
わがまま is more about selfishness or demandingness, often used for children or personal desires. 得手勝手 emphasizes acting according to one's own convenience, sometimes in a more calculated way.
A yojijukugo combining 得手 (one's strong point, what one is good at) and 勝手 (one's own convenience, selfishness). The exact historical derivation is uncertain, but the compound conveys the idea of doing things in a way that suits oneself.