According to Guardian, 8 in 10 who took the survey "say they understand their employee benefits very well to make informed decisions that can set them on a path toward employee well-being." But, in fact, most don't.

Meantime, employers are less confident about the ability of their employees to figure out their benefits package. Just 62 percent of employers say they believe their workers understand their benefits "very well."

But even employers are apparently wildly optimistic.

"Despite feeling overwhelmed by the increased complexity of their employee benefits programs, most working Americans claim to have a good understand of their workplace benefits," Guardian writes in the introduction to its report. "Unfortunately, their confidence level may be unfounded."

Twenty percent of those surveyed would have received an "F" if the survey had been a test using the generally accepted grading methods. While fewer baby boomers failed the test than other generations, millennials did worse than their elders, with 25 percent scoring an "F" on the exam.

More than half of all respondents — 51 percent — would have taken home a grade of C or below to mom and pop. 

Other findings proved disturbing as well:

• 25 percent say making benefits selections "is more of a guessing game than an educated guess;"

• 57 percent incorrectly think, when facing a critical illness, their benefits would reimburse them for lost income;

• The percent of workers who say "my employer does a good job of educating me about my benefits" fell from 66 percent in 2014 to 47 percent this year.

There were pockets of good news. For instance, 24 percent of all respondents did receive an "A" grade based upon their answers, and most understood what the term "deductible" meant. Nearly 9 in 10 knew the difference between accident insurance and auto insurance, and the same percent knew that not all costs associated with long term disability are covered by insurance.

But overall, Guardian says, the high percentage of mediocre to miserable grades are a very bad sign for benefits managers and plan designers, and the situation will likely become worse as politicians once more take up the cudgels to bludgeon each other over everyone else's health insurance.