I am reading Lighting Out For The Territory, a biography of Sam Clemens as a young man out West. He was a real prick. Much of what he wrote was untrue - not even exaggeration, but false reporting. His practical jokes were more cruel than funny, as was his writing in those days, and he carelessly caused a forest fire that took out half a side of Lake Tahoe for miles back. In the abstract, someone could make a case for the line between biting humor and just biting someone and calling it a joke being hard to see at a distance, but I don't think one can give him that benefit. He was insulting for fun, and often.
I'm not sure I'm going to read him with quite the same eye again. Life On The Mississippi is one of my favorite books, and this biographer credits it with being mostly true, yet his other works may not withstand this undermining when I read them.