Leaked letter says Peter Hendy was 'offensive' over Southeastern comments
There seems to be an unwritten, agreement in transport circles - do not slag off another operator's service.
There is an element of self-preservation in this, as usually it's only a matter of time before your own operation will face some kind of failure.
It also doesn't exactly promote a civilised image for the whole industry.
Well, the sometimes brash and outspoken Transport Commissioner Peter Hendy broke this code recently, when he made disparaging comments about Southeastern services and said the revenue protection officers were like "the Gestapo".
While some commuters were in agreement on the state of the service in and out of London Bridge, many employees were extremely aggrieved at his comments.
The RMT Union described his comments as an "outrageous slur".
And while they kept their counsel publicly, now it's emerged that the management themselves at the operator also took exception to the comments.
'Not good enough'
I have been given a letter to all staff at Southeastern from David Brown, chief executive of Go-Ahead Group.
In a strongly worded rebuke, he said: "The comments made were both unjustified and offensive.
"We immediately took the matter up with Peter Hendy and received a personal apology, but of course this wasn't good enough - we wanted an apology for you, the employees at Southeastern.
"I'm repeatedly impressed by your professionalism and the good service you provide. Once again at yesterday's London Marathon you showed how it should be done. There are lessons here for the Commissioner."
'Passion no excuse'
Since then the commissioner has apologised. He said: "I am quoted in Management Today being offensive about Southeastern trains and its staff. My comment is unjustified and excessive and I apologise.
"I know everyone there is doing their best to offer a good service in the context of the franchise you have and the infrastructure you operate on.
"If there is a context, the interview was several weeks ago during the worst of the issues at London Bridge. But that's not an excuse. Passion is no excuse for insult. Sorry."
The commissioner has made no secret of his desire to take over more of London's rail services, the temperature in that devolution debate seems to be rising.