First of all the language is foul, and cleverly strung together.
Especially the lines given to Calamity Jane.
I wanna dress up in chaps and dusters and wear a hat and call everyone mutherfuckninsunsof bitches and play cards and shoot up things with my gun.
It's Thug Life - Western Style.
Secondly, what other show will include a scene where the local heavy is so constipated that he has a whore wriggle her thumb up his bum in hopes of relief. Then have her give him a blow job.
And this is the scene where he then frustratedly tells the wench to "close up the ass flap" and I will admit I did NOT think he meant the back door to his Union suit.
Clearly, very authentic. And from what I can see, the writers throw everything in there, and any complaints - well hell, it's Deadwood, it's authentic!