This isn't that complicated, it's simply "treat others how you wish to be treated."
Before you proposition job applicants over Facebook DM just ask yourself: would I be okay with this if someone treated my mom/sister/girlfriend in this manner?
I'm not sure having sisters/wives/moms/brothers/fathers has much effect on people who are reared and imbued in a culture where entertainment (liberally defined) celebrates fraternity culture.
You just have to examine the "shaving cream on mouth and dicks painted on friends faces" attitude to know people do things to others that they _do not_ particularly want done to themselves.
To use a car analogy these are the kinds of people who would be happy to cut someone off while driving but would get enraged if someone did that to them. Of course, it's simple, drive defensively and don't do stupid things when driving --do people follow?
I know we are way past civics and other classes in school which tried to steer kids into a more "moral" frame of mind, but I think the advent of fraternity culture permeating into daily life beyond secondary education and educational institutions in the educated indicates that something's amiss in our culture.
Music, movies, games, etc., take a pretty jocular view of appropriate behavior --it's not to say there were not predators or other unsavory behavior by people toward others before mass media, but at least in some classes of people it was at least frowned upon whereas now it's openly celebrated with few exceptions.