The pilot is obviously behind the curve and either lacks situational awareness or could care less. If he was dealing with an emergency and slogging through his checklists I could understand him ignoring instructions, but just sitting there tying up both airborne and ground based traffic and ignoring repeated explicit instructions from ATC as he completes tasks he should have finished minutes earlier is at the very least extremely inconsiderate. He's lucky I was not the controller because I would have never given him a takeoff clearance after that, only to taxi back to the end of the line.