Nazi Bar

parable/meme about not letting any Nazis into your bar - These guys come in and it's always a nice, polite one. And you serve them because you don't want to cause a scene. And then they become a regular and after a while, they bring a friend. And that dude is cool too. And then THEY bring friends and the friends bring friends and they stop being cool and then you realize, oh dang, this is a Nazi bar now. And it's too late because they're entrenched and if you try to kick them out, they cause a PROBLEM. So you have to shut them down. https://en.wiktionary.org/wiki/Nazi_bar cf Tipping Point, social media (esp Twitter), virtual community