You know you're at kumoricon when you see multiple people who have dyed their REAL hair colors such as purple and blue.
Also, you know you're at kumoricon when wearing cat ears doesn't get you weird looks, but hugs instead!
And... when you are in constant fear of being hit in the rear with a yaoi/yuri/whatever paddle by a complete stranger randomly. (I saw a group hitting each other and ran... I was also Ritsuka at the time X_X )
... also, you know you've BEEN to kumoricon when you get back home and normal clothes look weird. XD