People are only resorting to Twitter because they don't get a response through other channels.
There needs to be a service that ensures an appropriate response at all times services are running, but particularly late at night when people are most likely to be drunk and rowdy. I would like a discrete sticker on every window of trains (and other public transport) with numbers to call or text in the event of antisocial or threatening behaviour, and assurances of a speedy response.
The sticker should include a unique reference for the train coach (or tram/bus) to quote in a call/message, and the operator should be able to identify the route and (hopefully) location, alert the driver, and if necessary arrange for Gardaí to meet the train at the next station.
I realise outside the major cities Garda availability is likely to be a problem.