Facebook has a rule about dating coworkers saying you have to succeed in asking them out the first time. You cannot ask again if they say no, meaning that female coworkers don’t have to feel pressured into accepting a date. They can simply say, “I’m busy that night,” and the person asking will have to be ok with that.
Google has similar rules about conflicts in that they’ll move things around in the office if a relationship creates a conflict of interest.