Today’s report, that Gaelic football referee Patrick Nelis has described how aggressive, personalised online abuse directed at him after last year’s Tyrone county final pushed him to try to commit suicide, is the latest in a long — and lengthening — list of examples of how the principle of manners, of self-control, of respect for others, or even basic restraint, have been swept aside by the remoteness and anonymity afforded by social media.