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