If you must say something unflattering about a customer, be careful what medium you use.
An acquaintance of mine runs a company that counts big, litigation-happy American corporations among its business partners. He has said that if he discovers any of his employees sending e-mail - even privately - to their co-workers, referring to any of these important partners as "fools" or "idiots", he will immediately fire those employees. His reason: When all is well, much can be smoothed over; but once business partners fall out and contracts get scrutinized for loopholes that will allow one party to renege on previous agreements, each will dig out everything it can to prove that the other was not a supportive business partner and did not fulfil its end of the bargain. Employee e-mails that indicate contempt of the other company can be forwarded carelessly or dredged up by IT experts years after they have been deleted, and waved about in a court of law by the company's overpaid lawyers to support that allegation.Think Twice
Perhaps my acquaintance leans towards over-cautiousness, but he does have a point: E-mail messages that currently seem harmless can be passed around and hauled out later, and used to build a case against the corporation that engaged the people who sent them. When you are about to send a message which spreads a rumor, includes comments that belittle a client, or passes on a fact that could be damaging to a client's reputation, think again. In view of what could be dragged out from the darkness into the harsh light of a courtroom, a whispered conversation with the co-worker you intended to send the e-mail to could be a safer option - provided your colleagues doesn't squeal.Off The Record
It's fine to have a disagreement on record, if the argument is based on what is factual and objective. Such disputes can be informative and help companies improve on processes. But if the argument descends into name-calling, uses "facts" from gossip circles, or raises information that is confidential (even if true), beware of conducting it in any recordable medium. Even gossiping about something that is factual, but still confidential, can be built into an accusation that one company failed to be a trustworthy partner to the other.As A Rule...
Never insult any client or business partner even in a private e-mail to a co-worker.
If a discussion gets heated, back off and couch your thoughts in objective terms.
Even if you are ready to leave your present company, communicate professionally about all its customers - if word gets around that you like to gossip about clients, few other companies will trust you with theirs.
When in doubt, refrain and rephrase.
If you must spew, do it face-to-face, and only with co-workers you trust.