Well, as much as I sometimes lack tact and prefer the blunt approach?
There's being an arse in general, and then there's just being a arse directly to someone's face. Maybe you should try simply being an arse over the internet, lassie! Sometimes people take that better, than in person. Decline to comment and say it in e-mail.
Ultimately, though, it's not you that has to wake up with the bastard, so it's on her and not you. This is also known as the "none of my bloody business what you do" code of friendship. You keep more friends, that way.