Glad you brought that up, he threatened me with one!
If the guy grabbed your finger and tried to injure it then you had every right to defend yourself. My question is why did the argument continue to the point of him inciting violence? Why not just walk away the first second the situation became heated? I would ask that question to both parties involved.
I know the guy, actually bought my guitar from him.. I thought we was joking around, until he grabbed my finger and started to twist it! (While talking alabama garbage).