Adjective. Combination of "adept" and "inept." It describes someone/something that has so much skill/experience with something that they perform poorly as a result, usually from thinking too much about the idea of what they're doing rather than the practical application.
My partner in my last game of Starcraft II was so indept. He was setting up an amazing late game build while forgetting that rushing is popular online. It's safe to say we lost.