Why not just draw him to one side and tell him exactly how you feel - ie that he seems be very negative to you - and ask him why?

Is he trying to help or hinder?

Does he hate storytelling? (I have a friend who positively detests poets, so any 'criticism' from them would always be unhelpful I would guess)

If he is doing it to help he'll understand.
If he is doing it to be destructive then it will confirm in your mind that he's an idiot and you can react accordingly in future.