My group and I have gone in and invaded threads without any real knowledge of the fandom or what have you. It's totally doable (and pretty fun, usually). Of course, that's always been in the context of broad multiversal-style setups. Well, not always, but most of the time. Also, there's always been a combative element to our antics. A mix of the RP fighting side and the straight storytelling. That might be one of the major reasons we've lasted so long. RP fighters are stubborn fucks. Wanting to compete and win really does tend to drive things forward.