@bibletruths Could he have perhaps had a negative experience due to that interaction where he had got scabs? Did he seem scared or stressed after that happened?
He could have had a bit of a negative interaction that involved his head, and both times, you stroked him there, and it re-reminded him of the stress/pain. Which would explain why he gave you such an obvious "No" signal.
It could also be adolescence. Some days, they just get extra grumpy, whether that's due to frustration or hormones. Perhaps he did it once on one of these days. You reacted in a way he wanted you to (You didn't move him and left him alone), and so he tried it again. It worked again, and it might be likely that he will try again in the future.
Or, as everyone else is saying, it could be pain. I definitely agree that taking him to the vets is a good idea (I saw you're already on top of that!) to rule anything medical out. Dogs show pain in strange ways, and being overly snappy is a pretty common one. If it is not pain, however, the two first suggestions are possibilities.
Good luck, OP. I hope your boy is alright and everything continues to be nice with him
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