A bad habit or vice — a habitual behavior that is undesirable and often worth correcting.
彼の悪癖は人の話を最後まで聞かないことだ。
His bad habit is not listening to others until the end.
悪癖を直すには本人の強い意志が必要だ。
To break a bad habit requires strong will from the person.
つい夜更かしするのが私の悪癖だ。
Staying up late is my bad habit.