Was Doyle bipolar?
In reference to the scene where Linda lets him back into the house, Doyle almost seems sincerely apologetic for a few seconds to wards Frank for the way he acted. It's almost like he knows his behaviour is bad, but when his mood changes he becomes a different person. And then not long after he gives a pretty faithful apology, he suddenly reverts back to his evil self by saying "but I got nothin to apologize for to queers and retards...." And then he checks himself and says "I know I shouldn't say that."
It's a very darkly hunourous scene, but it seems like Doyle has a Jekyl and Hyde thing going on that doesn't appear normal. I think Doyle had some mental health issues, in addition to being a drunk, and probably wasn't that different from Karl.
~ I'm a 21st century man and I don't wanna be here.