0. Start by moving the overton window to the edge of civility. Do not provide any justifications for your opinion. For example, "Protestors inside a government building should be met with violence"

1. Don't address any points they make

2. Make a snarky passive agressive response, thus winning.

3. Flag them for hurting your feelings. By discussing your ideas concretely ("who should perform the violence" "why?"), they have explored the "uncivil" aspects. This grounds for deleting their comment.