below the belt
US /bɪˈloʊ ðə bɛlt/
UK /bɪˈloʊ ðə bɛlt/

1.
卑鄙的, 不公平的, 人身攻击的
unfair or cruel, especially in a way that is too personal
:
•
His comment about her past was really below the belt.
他对她过去的评论真是卑鄙。
•
That joke was a bit below the belt, don't you think?
那个笑话有点卑鄙,你不觉得吗?