The story
Popularized by a July 2020 tweet by Michael B. Tager (@IamRageSparkle) explaining how he had once witnessed a bartender expell a non-disruptive customer whose "vest … was all nazi shit" because "you have to nip it in the bud immediately. 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 awhile 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 shit, this is a Nazi bar now.["]
Etymology from Wiktionary, CC BY-SA 4.0.