Why are woman so spiteful???

Is he referring to men or to women? I've noticed that women/girls can be very spiteful when it comes to a friends boyfriend. Whether it's because they want him for herself, they're jealous of the time spent with him instead of her, or just beacause they don't like him in general. Other than that I would say it's the wrong time of the month. I know that's a cliche but it's true - with me anyway.