It's always very unattractive when someone, leaving an organization or position, uses that opportunity to get their last "licks" in. For one reason or another, they are stepping down or passing the baton. In those moments when grace and class could really prevail, they instead discuss openly the frustrations that might have facilitated or motivated their departure. We've all seen it. The outgoing employee or leader inserts, in the midst of their last comments, observations about what they "just couldn't stand about this place." While the rest of us hang our heads in embarrassment for them, they leave the remaining dignity that they might have otherwise preserved tumbling around on the table like dice in a crapshoot.
I find that this practice is a violation of an unspoken "honor code." Not only does it dishonor the one that has been one's employer, but it also dishonors one's self. It suggests that this was a rotten place to seek vocational fulfillment and, at least until now, you lacked wisdom to detect it. It's a fundamental denial of your own abilities to perceive the landscape and anticipate the "potholes" that you might encounter. Listening to the final rant, we rightly wonder if you were the appropriate choice for this position in the first place. Your "parting shot" also dishonors those that will remain and labor to improve the organization or system you so venomously eschew.
Your "parting shot" dishonors those that hired you and expected your best efforts.
Your "parting shot" dishonors those that remain and seek to "enjoy the work of their hands."
Your "parting shot" dishonors you for shedding decorum and revealing your lack of poise.
When I witness this first hand, I typically just hang my head in shame; not on account of my own shame, but that of the one leaving. To observe someone shame themselves in this manner is an ugly thing to behold. I don't like to watch them shed their dignity in this way. Let them exit with grace and poise, and retain their honor even as they wisely (and quietly) move on from a position they should not maintain.