As an idea for bad blood, Kain (my character and leader of Gang B) could have had a disagreement with Damon (The leader of Gang A) when they both still worked together. Of course, I've always planned for Kain to be a bit bitter about some things, and this could be an idea to string off some bad blood between the groups. I imagine the argument between those two escalated to the point where Kain made his own gang to show Damon that he's just as good, if not better than him.
Kain is a bitter and petty soul. I just keep making him more and more mean. xD