Why does the cowboy stab the woman in Unforgiven?

Question

In Unforgiven,Why does the cowboy stab the woman in the beginning of the movie?

Was he crazy?

Answer 1

The woman is one of the younger prostitutes, working from the tavern. She upsets the cowboy by laughing at him - specifically giggling at his size.

When talking to Little Bill after the attack, Alice (the unofficial leader of the girls) says:

She's going to live. She didn't steal nothing. She didn't even touch his poke. Alls she done, when she seen he has a teensy little pecker, is give a giggle. That's all. She didn't know no better. Going to hang them, Little Bill?

(from the script) - thanks Clint

Its hinted that she is less experienced than the other girls ('she didn't know no better').

Answer 2

It was mentioned in the film that woman had said something unflattering about the size of the cowboy's 'equipment'. This angered him and he cut her up.