a teacher by negative example; a person whose bad conduct serves as a warning or lesson for others
那个总是拖延功课、最终成绩一塌糊涂的学生，成了我们班同学引以为戒的“反面教员”。
The student who always procrastinated on homework and ended up with terrible grades became a 'teacher by negative example' for our classmates, serving as a warning.
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