WASHINGTON – “Ferris Buellerism” is on the rise.

That’s according to SmartMoney, which recently put together a list of the 10 things employees won’t tell their boss.

Ferris Buellerism, that is, calling out sick for a decidedly unsick day, is apparently an ever-increasing trend in American workplaces.

With that in mind, the number one thing workers don’t admit to, SmartMoney says, is “I’m not really sick.”

According to a study by the Workforce Institute at Kronos, the number of employees who said they called in sick when they weren’t rose by 18 percent from 2006 to 2010. Interestingly, the trend is most common among companies that don’t offer paid time-off. For those who did, employees were far more likely to schedule days off in advance.

The second thing employees didn’t admit to was, “I’m just sick of working so hard.”

The Kronos study found that 62 percent of Americans who play hooky do so because they need a day off from the stresses of work. Amid the recession, many workers have more work to do and less people to do it. In that environment, employees say taking a day off from stress is becoming more common.

Another thing employees don’t admit to, “I’m very busy … updating my Facebook profile,” SmartMoney says.

While 64 percent of people admit to visiting non-work sites during work hours, that percentage is actually down 10 percent since 2008, according to a survey by Salary.com.

Here’s the full list of things employees won’t say to their bosses:

• “I’m applying for other jobs as you read this.”
• “My resume may be full of fibs.”
• “I’m starting my own business on the side.”
• “My bad mood is costing you money.”
• “I want you to be my shrink.”
• “I don’t want to be your friend.”
• “Money doesn’t matter. I just want you to be nice to me.”

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