That's quite a stream of thought for seeing one word in a post. It recall for a while you'd see "anti" on half-KIA for "anti-GG." It's just a generic grouping for people whose defining trait is their opposition to whatever group the speaker is assuming is their normal audiance. Could be anti-anime, anti-free-speech, anti-fan, anti-characters not as ugly as Concord, anti-just about anything. From OP context, there isn't enough information to tell.