1. be bad at 不善于。如：
I’m bad at maths. 我数学学得很差。
He is bad at playing tennis. 他网球打得不好。
2. be bad for 对……不好。如：
Too much salt can be bad for you. 吃太多的盐对你不好。
Smoking is bad for you (your health). 抽烟对你(你的身体)有害。
3. go from bad to worse 变得越来越糟，每况愈下。如：
His business is going from bad to worse. 他的生意每况愈下。
We’re hoping for an improvement but things have gone from bad to worse. 我们希望有所改善，但情况却变得越来越糟。