I own and love a grumpy, stubborn, moody horse. He is a perfect gentleman, very well behaved. He is in good health, no real reason to be a grouch, it's just the way he is and I love him no less for it. Everyone knows him in the barn as "the friendliest horse". He doesn't like hugs, he doesn't like kisses, he doesn't like being touched anywhere on his face. He is a rock, he is an island, and nobody is invited. Unless you have treats.
He is a great dressage horse, he gives a lot when you ask for it, but you need to be prepared to discuss it first. In many ways, he reminds me of myself. We are both loners, we don't like being bossed around, we don't like big emotional scenes, we don't like being bothered when we are in our own personal space, and for God's sake, stay away from our treats.
So bring 'em on! I think it'll be fun (and therapeutic) to hear everyone else's difficult child stories.