True enough, Rigsby is in the last few episodes, and thus the world will know what kind of a creep fuck serial killer he can portray on screen. HarvyHammer is wise in suggesting the great red dragon from this proper educated actor, Owain Yeoman. 
Rigsby has:
Daddy issues===
Women issues===
Self esteem issues===
friend/social issues===
A hidden past of humiliation where he was stripped and photographed by fellow students===
acrophobia===
profound out-of-character insight into the criminal mind shown to us on various occasions===
bizzare and unnatural respect for those that do not deserve respect.
One has to remember that Rigsby was questioned by LaRouche about the guy set on fire in the jail cell. No one ever confirmed it was Van Pelt's FBI football hero boyfriend. 
It's like this... Rigsby was a geek in school and was humiliated. He became a drug addict before joining Visualize (TV version of Scientology). Then, Rigsby becomes the great red dragon we all know as Red John and joins the bomb squad in San Diego and then later CBI where, coincidentally, Patrick Jane picks up his trail. The story from there is laid out before us. Red John is Rigsby, and Rigsby is merely the truth hidden in plain sight. No one makes fun of Red John, or they get dead! Think about it.