The excessive use of the nyan cat meme, to the point where the song becomes embedded in the central nervous system of a person. This is most likely to happen in Facebook wall posts or status updates.
Person 1: "Hey, did you see the new nyan cat video I posted on Person 3's Facebook wall?"
Person 2: "Oh yeah. It was absolutely hilarious!"
Person 3: (walks into room) "Oh my goodness I love nyan cat! nyan nyan nyan nyan..."
Person 1: "Man, you are totally suffering from Nyanception."