I feel like we have the same kid! Mine is generally very grumpy if anything at all has changed in his nap routine. Sometimes even if everything had been normal he's still very grumpy. He can go from happy to high pitched squealing type of cry instantly. He's very hard to be around. Lately the thing that makes him most upset is when we're reading stories. Nothing in particular sets him off, just the fact that the other kids want to sit and listen to me read.