How Dare She! Taylor Armstrong Mocks 'RHOBH' Costar Yolanda Foster's Lyme Disease -- Lisa Rinna Livid

Taylor Armstrong is back on Real Housewives of Beverly Hills, and she's already making a huge splash. RadarOnline.com has learned that during a recent taping session, she openly questioned the severity of cast member Yolanda Foster's debilitating Lyme disease, leaving costar Lisa Rinna furious!

A celebration for Lisa Vanderpump's husband, Ken Todd's birthday at their lavish estate, quickly turned cold as Armstrong "was openly questioning how sick Yolanda was," an insider told Radar. "Taylor said she was having major doubts about how serious the Lyme disease was for Yolanda, who wasn't at the party."

Meanwhile, "Lisa Rinna was openly seething with anger because Taylor doesn't even know Yolanda, and shouldn't have even gone there! It quickly became obvious to Lisa that Taylor is being brought back this season to stir the pot."

After the tense showdown, Rinna "has vowed to stay away from Taylor," the source continued. "She thinks she is just a huge opportunist."

Perhaps wanting to extend an olive branch after the awkward incident, Armstrong reached out to Rinna on social media.

"@lisarinna I just saw Lip Sync Battle @SpikeLSB #LipSyncBattle hmmmm...why haven't they invited us to face (I mean lip) sync it off? #RHoBH," Armstrong asked.

Rinna didn't respond to Armstrong, but the next day stated on twitter, "My mom always said if you can't say something nice about someone don't say anything at all. #fail."