Justin Timberlake is reportedly green with envy over his former GF Cameron Diaz’ new romance with John Mayer. Jessica Biel’s main squeeze was recently overheard making fun and mocking John Mayer while working out with his bodyguard and friend at Boston’s Sports Club/LA gym at the Ritz-Carlton Hotel.

When John’s track ‘Waiting on the World to Change’ came over the sound system a tabloid insider claims that:

“Justin started rolling his eyes and then mimicked John’s voice while his pal laughed hysterically. After a minute, Justin stopped, saying, ‘I really shouldn’t. I’m such a bitch!’”