Incorrigible

/ɪnˈkɔːrɪdʒəbəl/ adjective medium

So set in a bad habit that no amount of correction or punishment seems to fix it.

The incorrigible prankster kept rigging whoopee cushions even after three trips to the principal's office.

Memory Trick

'In-' (not) plus 'corrigible' (able to be corrected) — an incorrigible troublemaker simply cannot be corrected.