Near the beginning of my last "real" relationship, I responded jokingly to something she said with "don't ever piss me off." Apparently, though, there was something "in my eyes" when I said it that scared the crap out of her. In the year we were together I think we only had one fight and as soon as I raised my voice (which I rarely do in general) it was over.

To this day I don't know how I managed that "look", but something tells me if I could perfect it I could win fights indefinitely. And possibly frighten bears.