There Can Be Only One
Most poly people encounter a phenomenon where a heterosexual couple decide to open up just slightly, so that one or both members can have sex outside the relationship with women, but not with men. Most tend to call this a "one penis policy." I think that term is boring, so I've taken to calling it "Highlander Penis."
This is what happens if another guy has sex with your woman
Needless to say, I find it incredibly frustrating, not only as a man who slogs through the dating world, but also because it almost always seems to rely on sexist assumptions about the difference between men and women. Whenever I encounter it, I just roll my eyes and think of this: