"Simon is a pompous little (expletive) who walks like he has a stick stuck up his (expletive)," Osbourne told The Sun.
The battle goes back to when Cowell called Osbourne's daughter Kelly "ugly" and said Ozzy Osbourne staged his near-fatal quad bike wreck to improve his record sales, the New York Post reported Thursday.
Cowell later apologized, but the hard feelings apparently have not subsided although the pair are set to star on "X-Factor," an "American Idol" type talent search.
"Ozzy is furious I'm doing 'The X-Factor' (with Cowell). He wants to rip Simon's head off," Osbourne said.