[samhw]

I think the other person got it spot-on in their reply. It's not about social pecking order - a long-time employee could well be at the bottom of the social pecking order - it's about whether it's perceived to be your own work that you're deprecating, rather than their and not your work. It doesn't matter if it's someone else's too, only that it's yours in part.

This is closely related to the ingroup vs outgroup distinction, but not quite the same: e.g. I could be a former employee, even someone who was disliked or who left in disgrace, and still be under the aegis of the 'us' in this context.

Edit: On reflection, I kinda ignored the rest of your message and got stuck on the answer to your clarifying question. I do totally agree with your point about maturity. I suppose my only caveat is that I was moaning/joking/joking-and-moaning at the time, rather than making a serious point that would have been relevant to our work, so I don't think it was immaturity in a sense that caused any actual problems.