How they react to slapping them...
Ragnar:
When your palm hit his cheek, the impact of the slap forcing his head to the side, he would stay still for a moment. Although, as quickly as It happened he spun around grabbing your wrist. "Now, what was that for?" He smirked.
Rollo:
Rollo would be stunned, mouth slightly hanging open in surprise. Then a loud laugh would erupt from his chest, causing him to get slapped for the second time.
Floki:
Floki would be upset. Not because you slapped him, but because he genuinely didn't know what he had done wrong.
Athelstan:
The moment you slapped Athelstan, he would apologise for whatever possessed you to do so. He would also pray to god for forgiveness.
Bjorn:
Bjorn's reaction was much like his fathers. Shocked, but also amused at the fact you actually slapped him.
Ubbe:
Ubbe would become rather upset, sitting down on the nearest piece of furniture before saying it was ok. Then asking to talk whatever it is out with you.
Hvitserk:
The look Hvisterk gave you when you slapped him was quite scary, he seemed mad. Then a loud burst of laughter would echo throughout the room. "I'm sorry, can we just talk." He laughed.
Sigurd:
Sigurd would be upset that you slapped him but decided against showing it. He wanted to sort through your argument instead of getting slapped in the face again for complaining.
Ivar:
He would be mad, warning you that if you ever did it again then there would be consequences.