Others have given the premise to the story so I'll just dive in... even if we buy into the belief that a murderous band of cutthroats, killing everyone in the haberdashery but leaving Bruce Dern alone is beyond far fetched; he'd be dead too if were in real life... but he needed to live so fluke of all flukes, the man who killed his son (Samuel L Jackson) happens to arrive so he could goad Dern into a fight and killing him giving one of the gang time to poison the coffee... contrived much?
Then, Oswaldo (Tim Roth) , out of the blue, asks 'which one has a letter from Lincoln?'... how would he know that? That little tidbit was shared while on the stage and Jackson's character was a rider they just happened to pick up on the way.
When John Ruth (Russell) realized he was poisoned, instead of pulling his pistol and killing Daisy (Leigh), he starts beating her up... that makes zero sense.
Tarantino makes an over the top violent piece of crap that takes three hours to watch... only reason I gave it the time to watch was I was home sick and it filled in the time... I wish I had sat on my back porch and watch the birds instead... this movie is just plain awful!