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By Kat Giantis

With two months to go before she hits the big 4-0, Denise Richards isn't showing any signs of growing out of her bad-boy phase. After reportedly spending Thanksgiving with ex-husband Charlie Sheen, the blonde is now being linked to Motley Crue bassist Nikki Sixx.

Yes, it seems Cupid has been overindulging in the Zima again.

Us Weekly says the longtime neighbors have started "quietly dating," and on Dec. 12, they were spied enjoying breakfast together at a Calabasas, Calif., café.

"Nikki was telling stories," relays a spy, "and Denise was laughing."

You'd think that Richards would be a little gun-shy about dating too close to home. After all, she had an infamous falling out with onetime neighbor and friend Heather Locklear when she hooked up with the small-screen star's ex hubby, Bon Jovi guitarist Richie Sambora.

But a source tells the mag that Denise and Nikki, 52, have "a lot in common," which presumably extends beyond both having questionable taste in partners (his most recent ex is Kat Von D, who's now with Jesse James; he also has two Playboy model ex-wives).

They're "getting to know each other slowly," another insider assures PopEater, adding that Richards isn't fazed by Sixx's colorful, heroin-filled past.

"Yes, he is a recovering addict," says the source, "but he's also a great dad and has no history of violence!"

Pardon us while we introduce our forehead to our desk. OK, moving on ...

Denise, who has two daughters with Sheen (Sam, 6, and Lola, 5), tweeted birthday wishes to Nikki the day before their breakfast meet-up.

A few hours later, the rocker teased about a "midnight rendezvous" with "a beautiful maiden."

He also publicly wondered a couple days earlier why Denise was "so distracted": "Its not like you have a million projects,2 daughter's and are remodeling your house,anything else:)?"

Richards' rep did not respond to our request for comment on the dating rumors.