Unfortunately, no matter how much time you put into the hiring process, every once in a while a toxic employee is bound to slip through your HR department and into your work force. And that's a problem. Research shows that good employees are 54 percent more likely to quit when they work with a toxic employee.

While it would be great if toxic employees came with a big TOXIC stamp on their foreheads to warn you of their presence, that's just not how it works. Instead, you've got to figure it out for yourself. Sadly, that often means that a lot of damage can get done before you actually figure it out.

So, what exactly are the warning signs that you've got a toxic employee in your midst? Here are 7 you should keep an eye out for.

1. Harasses and bullies others.

I can guarantee that none of your employees look forward each day to being bullied or harassed by their co-workers or boss, but it's something toxic employees are very good at doing.

2. Always blames everyone else for their failures.

Isn't it funny how some people always think that every problem they create--every mistake they make--is someone else's fault? That's delusional on their part, and a sure sign of a highly toxic employee.

3. Other employees don't want to work with them.

When your employees tell you they don't want to work with a particular co-worker, chances are very high that you've got a toxic employee.

4. Customers ask you for a different point of contact.

When your customers tell you that they don't want to work with a particular employee, then you know you've got a real problem--one that can hurt your bottom line and that requires immediate action.

5. Supports co-workers (and you) in public, tears you down in private.

Highly toxic employees love to work behind the scenes to do their dirty work. They have no problem at all telling you to your face that they think you're great--at the very same time they are telling everyone else you're a complete loser.

6. Is a drama queen (or king).

Highly toxic employees love to create drama--as much as possible, when you least expect it. For them, it's a spectator sport.

7. Has a bad attitude, and loves to spread it around.

While no one can have a good attitude every single minute of every single day, toxic employees seem to have a bad attitude all day long. Not only that, but they are never truly happy until they put everyone else in a bad mood, too.