Lovingkindness meditation is the practice of taking an interest in and caring about ourselves and those around us. Lovingkindness meditation usually works in stages. You start with yourself, then express lovingkindness to a friend or a family member, someone you are already kindly disposed to. Then you do the same with someone you don't know very well or people who you occasionally run into and take for granted. And finally, you express these same feelings of understanding and empathy to people you don't like very much.
The aim is not necessarily to begin liking them. The aim is just to begin recognising that those people have their own struggles, just like the rest of us. When we practice lovingkindness, we recognise that everyone wants to lead a happy, healthy life. Even those people you can't stand.