I belive Red John might be Patrick Jane's father.

There was a murderer who Jane provoked to offend Red John and RJ killed him afterwards. The reason was the exact reason that provoked Red John to kill Jane's family. Only this time, RJ killed the offender, not his family. So why would Patrick Jane be spared? Because a father cannot kill his son.

Also, one might agree that for a serial psychopathic murderer there would be some fun in playing games with a smart cop, but Patrick Jane is, indeed, a pain in the ass for anyone trying to commit crimes. So why keep sparing him? Why, instead of getting rid of him, RJ keeps trying to get him on his side?

Thirdly, Patrick has mentioned that Red John is someone better than him at cold reading and stuff alike. We've all seen, in Jane's flashbacks, that his father taught him how to do everything he knows. So one better than PJ is only his father, having the advantage of knowing his son's patterns and everything.