How about this "You raise a really good point, but let me think about it for a while, okay?"
Or, leaving a friend's, if feasible, you could stay. Or, at friend's ask him "Why he would like to go?" If he gives you any response (I am tired, I feel uncomfortable, I am bored etc) then you can grant his request-if this is a behaviour you want to change in H.
He will need to give valid reason for something he requests, if it is a point on which you disagree. Although hanging pic, is minor, unless on ceiling or over bed and could impale S in his sleep...lol.
I realize you may see this as giving in. But if he or you, cannot meet in the middle at this point, then giving H the tools with which to have his request granted will lead to a little security and safety in his mind (he is making decisions, you are listening) and then you can move from there.
I have a hunch he is so used to you disagreeing that the "Do it my way now" is a reflex...easily changeable, btw, with a little work and swallowing of pride
