If the Diogenes Club and Fight Club had an intermittently gregarious baby, it would be The Gastonia Society for Free Thought. People come here to discuss all the things forbidden by polite society. No topic is off-limits, just be ready to defend your views with evidence. This is an atheist-friendly group, but it is independent and unaffiliated from all other organizations. This is "disorganized" atheism free of obligations, sociopolitical litmus tests, or agenda. No attendance is taken, no RSVP's are required, and no solicitation will be made. You don't even have to join the group officially, just show up if you are so inclined.
Pro-Tip: Don't solicit or proselytize. Don't run your game here, people.