A Bitch Streamer is a YouTuber or Twitch streamer that is Bisexual or a Bisexual Ally. This term is of course satire, as indicated by the usage of the word Bitch. The term is often used to troll Twitter users.
Twitter User 1: Hey did you hear that Joe is a Bitch Streamer?
Twitter User 2: Really? That's amazing!
Normal person: *laughs their fucking ass off*