You need to side with Mirage and after go to the wastelands and explore. You should get a invite from the Skullbreakers. Now just slut yourself to the tribe.
I got it even after defeating Mirage. When you go the Skull breakers camp, be naked and always choose submit to enter. And have fun with the outdoor prisoners. You're respect will drop enough, and then go talk to Khalgor.
I don't how to do it if you side with Mirage though.
