It's the workplace fantasy almost everyone has had at least once.

You're about to leave your employer on less than favorable terms. Maybe you didn't get the promotion you wanted, or your idea for a new revenue-generating project was shot down. Or perhaps your boss really has it in for you. So you decide to leave in a blaze of glory--with a letter that really "speaks truth to power."

Jeff Shane's advice: don't do it.

Shane is president of Allison and Taylor, a Michigan-based firm that frequently digs people out of the holes they dug for themselves when leaving a job. He says he's seen way too many incendiary letters.

"It's very easy to lose your perspective. And many people that are leaving on less than favorable terms believe rightly or wrongly that the employer is to blame," Shane says. "Their attitude is, `You know what, I've got nothing to lose. I'm going to give them a piece of my mind.'"

The result is often a letter that makes the writer feel good for a day or so--until reality sets in.

(On the flip side, learn how CEOs like Jack Welch fire people from Radiate)

"They don't stop and think that somewhere down the road, they are going to need their former employer to get a new job," Shane explains. "If you burn your bridge [with your former employer] could come back to bite you."

Shane's firm is often called in to clean up the mess left by a remorseful ex-employee. Allison and Taylor can conduct reference checks to see what a former employer says.

"If the information offered by the reference were unfavorable, which is true of about half the ones we talk to, then the client would be able to use our report for some sort of remedial action," Shane says.

That might involve a cease and desist letter, warning the ex-employer not to offer up such negative commentary again. Shane says the success rate of those letters is extremely high. The best outcome may be one we're all familiar with: a prospective employer calls your old place of business, and gets a supervisor who says all the company can do is confirm your title and dates of employment.

Shane calls that a "no-harm, no-foul reference."

So how do you avoid putting yourself in that situation? Shane offers up examples of two letters you could write.

If you're resigning due to bullying, harassment, age discrimination or sexual overtones, the letter might start like this:

 "As you may or may not be aware, some members of your management team do not adhere to appropriate company policy. Accordingly, I regretfully tender my resignation having experienced unsuitable corporate behavior."

Or, if you are resigning due to the always-popular "philosophical differences": 

"Please accept this as my official notice of my resignation. As you are aware, over the last twelve months we have had numerous differences of opinion regarding best practices and goals for the company's X project. Unfortunately, it is clear to me that you and I will be unable to resolve our differences. Therefore I feel that my resignation is the best option for the team and all concerned."

Shane says when it comes to writing a resignation letter--no matter what the circumstances--there's one thing you absolutely have to do. 

"Write the letter, put the letter in the drawer for a day and then look at it," he says. "Then ask yourself--is there any way this letter is going to make my life miserable at a later date?"