Should you say congratulations if don't like someone?

You should say congratulations to a person if they do something good if you don't like them. If they are just mean back, you can ignore them, if they are just annoying, deal with it, it's not like they are hurting you in any way.

It's good to be nice to other people, remember, do unto others as you would have them do unto you. (translation: treat people how you would want them to treat you.)