I would say he is doing it because he's knows its causing you both to be stressed. The fact that he's intelligent would back that up, he may have intended it as a one off but seen how effective it was at upsetting you so continued. Your statement 'he's ruining family life' seems significant, it could well be his aim so what is more important than stopping him from doing this is to find out why he feels the need to gain your attention in that way. (Maybe he has hopes of his parents getting back together and sees you as an obstacle or if he's new to being your stepson perhaps he's testing you out? Could be any number of reasons) If you don't look for the cause you may find that you stop him doing this only for him to find a better tactic so I'd say concentrate on that over trying to put a stop to it.