Complaining without Carping
At times, it's necessary to complain: if we tolerate a behavior or a situation without making any remark, the other parties will assume that everything is fine and the pattern will continue. However, complaints must be tendered carefully to avoid being seen as a whiner.
First of all, complain with a purpose. You should make it clear what the problem is, why it's a problem, and the resolution you want to achieve. Otherwise, it will be perceived that you are just venting.
Also, complain to those who can make a difference. If there's nothing a person can do to rectify the situation, there's no point in complaining to them about it.
When complaining, be descriptive and factual, but not judgmental. Indicate what occurred, not what you assume the other party's motivation to have been, and be as neutral as possible (as opposed to showing your anger and frustration).
Finally, suggest a specific solution. If there is nothing you expect to gain by complaining, then there's no sense in raising he issue at all.
Also, it's important to provide positive feedback when things go well (or better than expected). If you only speak up when something is "wrong," you'll be labeled a complainer.
EN: Other guidance from elsewhere: consider complaining to be in the same vein as criticism. Complete avoidance will result in failure to rectify a problem, but doing it too frequently is seen as a character flaw.