(Image: AAP/Dan Peled)

The only way to effectively combat graffiti is to immediately erase it. The theory, which does work (I’ve tested it), is that denying the graffitists the physical proof of their work is the thing most likely to dissuade them from bothering again.

The same (tested this too) applies with online trolls. A policy of never engaging, never replying, treating them with the absolutely silent disregard that they have earned, leaves them in their echo chamber, alone and irrelevant.