Yes, I was retarded enough to attend one of their meet-ups. The funniest thing was that I probably behaved like the most autistic one there, since I mostly tried to avoid contact, once I relized what a bunch of cringelord they were which was pretty much immediately. There were wearing an astonishing amount of mlp merch, and half of them brought plushies and toys, the amusing thing was, however, that they didn't even talk about the show at all, and talking about the show was the only reason I decided to go there in the first place.
There was one autist, who came with his caretaker or something, who I had a misfortune to talk to. He spend like 20 minutes telling me how emotionally impactful Adventure Time was for him and that he even cried watching one of the episodes that came out somewhere around that time, after that he went on tangents about some retarded tech stuff I couldn't give less of a fuck about, it seemed like he didn't care about the show that much at all, and any and all of my attempts to change the subject to it failed miserably. There was also one dude who looked like he was in his mid to end 20s, but who behaved like he was ten. I legit think he might've had some sort of mental impairement, but nobody seemed to give a fuck.
That being said not everything was all grim and gloom, there was also that one dude who was fairly decent guy who I spend most of my time there talking to. We talked about the show and games, and life, and stuff. We even exchanged contacts, but being an autist that I am, I eventually stopped talking to him and deleted him.