Yes its unacceptable behaviour but who exactly gets through their twenties without the odd incident? I think its wrong to make a big issue of this. It happens. Fine them and get on with it. Its only a problem if it becomes persistent behaviour. Anyway, better to piss on a pitch than piss all over the game as England have done this series.But they were in public view, and not behind closed doors, hence why we all know about this little incident in the first place. This wasn't a case of paparazzi hiding in bushes and peeking through windows, they were able to observe all of this happening in plain site. This was in no way a "behind closed doors incident". The journalists that broke the story did nothing more than they were entitled to, there have been no suggestions of foul play or dishonesty, which as far as I can tell is what you seem to be alluding to.
In any case, at the time of the incident they were all kitted out wearing their whites with the England badge on the chest. If they aren't representing the country whilst they've got the three lions emblazoned upon them, I don't know when they are.
But even if we can accept that this was a private party - which it obviously wasn't, even with the most liberal interpretation of what is meant by private - and that they should have no more expectations placed on them than anyone else, their conduct still falls below what would be considered acceptable of people in the majority of situations, regardless of who they are.