Credit: Unsplash/CC0 Public Domain On April 26, a five-month old Twitter account with the handle @LegacyChaser369 pinned a tweet to its profile that began: “The Proud Boys are back on Twitter! #NewProfilePic #POYB #Westisthebest #Uhuru #maga” The pinned tweet, which sits atop any other posts, was practically a glossary for the language of the extremist street gang known as the Proud Boys. But if the insider terms weren’t clear enough, there was the banner image: A group of Proud Boys holding their hands in sideways “OK” signs, a known rallying symbol for white supremacy. Twitter, citing its policy against violent...