a hard nut 冥顽不化的人;无知无觉的人
A:Bob refused all his classmate’s invitations.
B:I really couldn’t understand him.
A:He’s surely a hard nut, nobody likes approaching him.
B:We’d better also leave him alone.
甲:鲍勃拒绝了班上所有人的邀请。
乙:他这个人我真不明白。
甲:他真是个脑子不开窍的人,没人愿意靠近他。
乙:我们最好也别惹他。