When someone loves tetris so much that playing it or fantasizing about it become the only ways that they can get aroused. Many people with this fetish get off with one hand while playing tetris with the other.
Guy 1: "That girl I was with last night kept telling me I had a nice line piece and she yelled 'tetris' when she came."
Guy 2: "Yeah, I tried to tell you she has tetrisphilia."
Guy 1: "She did insist on having the song 'Korobeiniki' playing while we had sex..."