If a guy is bashing some woman behind her back saying all sorts of awful things but to her face is being all nice and flirty with the sole goal of f**king her then dropping her, you're getting no "bro code" from me. I will absolutely out you.
I have no problem with hook ups at all, but if you're going to act like a scumbag, I'm going to treat you like one. I don't care if that's labeled as white knighting or whatever the f**k. It's not even about gender, if somebody is being super phony trying to take advantage of somebody else, you have zero respect from me and I will burn you to the ground in whatever way available to me.