In fact BS is the reason in this case.
Apparently Obama and Douglas Brinkley, who wrote the article were speaking with Rolling Stone executive editor Eric Bates, who said that his daughter told him to tell the president, “You can do it.”
Obama reportedly grinned and said, “You know, kids have good instincts. They look at the other guy and say, ‘Well, that’s a bullshitter, I can tell.'”
White House Communications Director Dan Pfeiffer was asked about the comment Thursday in Richmond, Va., and said the issue was about Romney’s “trust.” He said people should “not be distracted by the word” but to “focus on the issue.”
The Huffington Post points out that President Obama is not the first candidate to curse: then-candidate George W. Bush called New York Times reporter Adam Clymer a “major league asshole” over a hot mic, to which vice-presidential nominee Dick Cheney agreed.