At this discussion board I occasionally frequent, completely new inquirers sometimes post saying, "I'm thinking of visiting an Orthodox parish this Sunday, it's called St X in $CITY. Does anybody know anything about it?" The correct response is not, as some people apparently think, "That doesn't, upon a cursory examination, look like it's a bunch of schismatic liberal fakers pretending to be Orthodox. They're Greek, though, so you'll probably suffer extreme culture shock."
Proper Response: either silence or, "I once stayed a month in that town and the people were amazing," depending on what the case is. If nobody else pipes in and you know it's not a bunch of schismatic liberal fakers, you can say, "Sounds great, I'm glad you'll be going there," or something else generally supportive.
Under no circumstances, save when they have actually run into them, mention bizarre vagante groups. I also recommend against FM-G's "12 things..." guide because it really sucks, but, lacking better material, it may be acceptable. Part of the problem with it is the problem with the first response: acting like the whole thing will result in a giant case of culture shock because it's bizarre and foreign. Grant that the thing might be bizarre and foreign. Don't treat it like it is. Orthodox worship is natural to the people who do it, it's what they do. Present it as such. Essentially say, "Here is what Orthodox worship is like, it's not weird, they're doing what they do: it's what they do." To say, "Here is what Orthodox worship is like, I know it looks really weird to you, but you might get used to it someday or something," is a grave mistake.
I hope this short note helps correct some of the errors I have seen others fall into. Be glad that these things you (perhaps not you, Dear Reader) fall into are mere misstatements and blunders, and not sins, as is the case with my failings.