I have a strong intuition that countering bullying with violence only works with disproportionate violence and/or public humiliation. It's almost like there needs to be a situation in which either the victim turns the tables in a spectacular way in public, or responds with violence that is shocking and disturbing.

In other words, I feel like the "snapping" is just as important -- if not more -- than the violence, per se.

I'm reminded of an anecdote which I think is attributed to Robert McNamara. Basically, he claims that a nuclear power shouldn't appear too rational. Adversaries should be left with a sense of "they're just crazy enough to use it". I think the same goes with bullying: "he's just crazy enough to actually kill me over this".