Why would a guy friend bite a friends arm?

I was hanging out with my guy friend today and I guess he was getting kind of flirty. I was trying to help him with some work and he pulled my face close so basically are lips were touching. He grabbed my arm and bit it and he did it too hard and he said he was sorry and he thought it left a mark. He ended up doing it again on both arms where he left marks. Why would you bite someone's arm?
Why would a guy friend bite a friends arm?
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