London: `X-Factor` boss Simon Cowell embarrassed American guest judge Nicole Scherzinger by getting her to call contestants a "tool".
He told the Pussycat Dolls singer it meant someone had a good voice, when it is really slang for a fool, a news website reported.
Scherzinger, 32, who is dating British Formula 1 ace Lewis Hamilton, used the word to describe wannabes at the Manchester auditions when she was trying to praise them.
Cowell eventually stepped in to tell her what it really meant leaving her red-faced.
"Simon loved winding Nicole up. Even though she has a British boyfriend she had never heard the phrase before. Simon eventually had to step in when she kept using it about people she liked," a source said.
Scherzinger was on the panel in place of new mother Dannii Minogue, although no guest judge was brought in for malaria-stricken Cheryl Tweedy.