someone who is beyond reform, instruction, or improvement; often used to describe a person lacking character or potential

面对这个屡教不改的学生，老师失望地感叹道：“真是朽木不可雕也。”

rotten wood that is too decayed or brittle to be carved into anything useful

这根木头已经烂透了，可谓是朽木不可雕。