People around him are disgusted by his selfish behavior.
You should change your self-centered way of thinking.
利己的 is a formal, abstract term for egoistic or self-interested behavior, while 自分勝手 is more colloquial and describes everyday selfish actions.
利己的 is a formal, analytical term for egoistic behavior, whereas わがまま is the everyday word for someone acting spoiled or demanding.
利己的 is a more formal, analytical term for putting one's own interest first, while 身勝手 is the everyday word used to criticize someone's selfish behavior.
selfish gene
Compound of 利己 (self-interest) and the adjectival suffix 的 (-like, -ish). The term 利己 is itself a Sino-Japanese word meaning 'benefiting oneself'.