Mine has got to be those evil video games.
I enjoy them from time to time too, but it still drives me crazy how completely he gets sucked in. He will stay on them for days upon days and seemingly forgets everything else (laundry, dishes, eating). I understand needing to concentrate on a game but for that long? And trying to catch his attention to ask a question? Not gonna happen.
He acts like interrupting his game is the end of the world. A life or death situation.
I had hopes when we first met that he might grown out of them (even just a tiny bit), but after meeting his family it's clear that's never gonna happen. His brother and father and exactly the same way. :'(
Seems so completely common, but still crazy making.