Anyone who has travelled on the Enterprise train from Dublin to Belfast at night more than a handful of times over recent decades will have encountered drunken passengers.
For a long time, such drunkenness seems to have been tolerated by the authorities as one of those facts of lives: that people leaving a major capital city to return home at night will sometimes be the worse for wear.
And so, it seems, little is done to combat bad behaviour and drunkenness.
Translink says that only alcohol purchased on board can be consumed, which suggests that passengers are not allowed to board with alcohol.
But do the train companies have enough staff at Dublin Connolly station to prevent such people?
How are they able to cope if groups of passengers who are refused boarding get aggressive?
Is it easier therefore just to let them get on the train, and hope all will be well?
On Saturday evening, as rival GAA fans travelled home from a Croke Park fixture there was over-crowding and violence.
According to witnesses, there were passengers on board with crates of beer and bottles of vodka.
On this occasion, there was what Translink described as “an affray” on the journey towards Northern Ireland.
Someone on board felt that they needed to press the emergency stop button and the police had to be called to resolve the situation.
There seems to be a persistent failure by the train companies to protect the right of the majority of passengers who just want to travel in peace to be able to do exactly that.
Until a zero tolerance approach is adopted to excess alcohol, with the full support of both cross-border train companies and both police forces, and a clear understanding that offenders will be heavily fined, this kind of incident will recur again and again and again.