An inveterate bullshitter.
Somebody who couldn't tell the truth if their life depended on it.
Zebu, meaning deception or lies comes from the practice of unscupulous restaurants saving money by passing off imported, tough Zebu meat as proper domestic steak.
Steve: That Hillary Clinton is such a liar. Said she'd been under sniper fire in Bosnia when she hadn't.
Fran: Yeah. And she claimed she was named after Sir Edmund Hillary, even though she was born five years before he climbed Mount Everest.
Steve: Don't forget when she said she was a fan of the New York Yankees, even though everyone knew she came from Chicago and supported the Cubs. What a liar.
Fran: She isn't just a liar. She's a real Zebu farmer.