Bad KARMA’s does not only include bad action but Bad Thoughts also. Its really very difficult to follow this principle. It does not mean you have to think good of people you hate. It means you just stay neutral about them, Just dont think any thing bad about them. The bad thoughts , meaning cursing, swearing about them in your mind, emit negative energy and will be counted as a Bad Karma in your own account.
Following this principle is the first step to salvation and self improvement.
Follow it , you will instantly start feeling good. You will instantly live a stress free life because you are not accumulating any bad Karmas.