I think a lot of people are assuming a history of this sort of behaviour. If this was the only time this guy acted like this, then yeah, it would be an extreme overreaction, but this guy has probably been a massive douchebag for years, and pushed this woman to her breaking point. Still doesn't make it ok, but I think it makes it understandable why some would be pushed that far (and the alcohol and drugs probably helped dull any inhibitions as well)