degenerate ex-student; failed student; dropout
Derogatory term for someone who has left or failed out of school and is seen as having fallen into a dissolute or aimless life. Often carries a judgmental tone.
He's a degenerate ex-student, now just drifting around without a steady job.
Compound of 学生 (student) and 崩れ (from 崩れる, to collapse or fall apart), literally 'student collapse', implying a student who has fallen from the expected path.