BANG!

Without warning, the rifle discharged, tearing a hole through the floorboard of the car of an Army colonel. The rifle belonged to a young lieutenant who had been invited to go hunting with the colonel.

Though no one was hurt, the incident left everyone in the car shaken. Worse, the lieutenant hindered his own promotion, according to executive coach Bruce Sillers, who was a member of that same battalion at the time of the incident.

You may never have committed as grave a faux pas as this lieutenant, and if so, be thankful. Nonetheless, we're all capable of making mistakes that can send us straight to the career doghouse. Here are five big no-nos to watch out for.

1. Sending inappropriate e-mail

Most of us are bright enough to realize that chain letters or off-color jokes have no place in business communications. Where most office workers get into trouble is with the over-hasty e-mail reply.

Ever read an e-mail too quickly and fired off an angry reply, only to discover later that you had misinterpreted the first sender's message? You end up not only wasting everyone's time, but poisoning your work relationships -- perhaps permanently.

Before you reply to an e-mail that has elevated your blood pressure, apply one of these useful tests: Ask yourself, "Would I feel comfortable explaining my response on a witness stand?" or "Would I want my response to be published on the front page of The New York Times ?"

If the answer is no, take time to cool off. Store the message in a drafts folder and review it later. Are you sure this is what you want to say, especially if you're directly insulting the recipient? Can your words be interpreted more negatively than you intended? And finally, would you want this message to find its way to your boss -- or to the HR director?

By the way, don't rely on any "unsend" feature, either. That feature will fail when you need it most. And be very careful of hitting Reply All -- or your supposedly personal conversation could be the talk of the office.

2. Putting down co-workers

Having done a significant amount of work for a particular client, I decided one day to try to expand my presence there. I called an executive in another part of that organization, introduced myself and said that "Carl" (a fictitious name for the IT executive with whom I had been working) was pleased with my work.

That executive responded, "Why should I care what Carl thinks?"

Not smart -- especially when said to someone outside the organization. If Carl had heard about this remark -- and these things do get around -- it could have created a Grand Canyon-size rift between him and his indiscreet co-worker. More critically, remarks like this damage the credibility of the organization.

Here's another example: Suppose you're the person the help desk elevates problems to when they are unable to resolve them. You find out, while talking to a customer, that the staffer she talked to gave her some really poor information. At this point, you may think the staffer is an idiot, but it's not a good idea to say so.

For one thing, if word gets to your boss that you're bad-mouthing your co-workers to the customers, you could be in big trouble. CIO Denny Brown of US electric utility provider Arizona Public Service makes no bones about it: Such behavior constitutes insubordination, and therefore is "grounds for termination," he says.

It's a much better idea to maintain a united company front when dealing with the customer. Resolve the issue with your IT colleague privately.