To be on bad terms; to have a poor or unfriendly relationship with someone.
私は彼とは仲が悪いので、できるだけ関わりたくない。
I'm on bad terms with him, so I want to avoid getting involved as much as possible.
隣のクラスとは昔から仲が悪いらしい。
It seems our class has been on bad terms with the neighboring class for a long time.
二人は仕事のことで仲が悪くなった。
The two became estranged over work issues.