Former "Hills" star Audrina Patridge celebrated her 27th birthday at Wet Republic at the MGM Grand yesterday ... by donning her customary two piece outfit.

Like some parts of Audrina, seeing her in a bikini never gets old.

Former "The Hills" actress Audrina Patridge took time off from her busy schedule of wearing a bikini in L.A. ... to show off her slammin' body in a white hot bikini at the ME Cabo Hotel in Mexico yesterday.

Audrina is down in Cabo San Lucas celebrating her 27th birthday with her BMX boyfriend Corey Bohan and some family members.

All of Audrina has grown up quite nicely.

Former MTV star Lauren Conrad is back on "The Hills" -- Beverly Hills -- because she just dropped $1.35 million on a swanky new condo in the wealthy L.A. neighborhood.

The ex-reality star will be the newest resident of the 90210 -- recently purchasing the massive 3,200 sq. ft. 2-story, penthouse condo with 3 bedrooms, 4 baths, and a 24-hr security system ... to keep away all those crazy "Hills" fans.

The house also sports a rooftop pool, outdoor deck, full gym, indoor bar, marble bath and hardwood floors.

But all this doesn't come cheap -- Conrad has to shell out $2,319 in homeowners' fees alone ... and then pay her million dollar mortgage on top of that. Oh, and this is her 2nd house -- the other one is in Malibu.

All hail LC.

Kristin Cavallari has some problems back on the home front ... because her family has officially lost their ocean-front mansion featured on "Laguna Beach" after falling behind on mortgage payments.

The house is INSANE -- 5 bedrooms, 5 baths, ridiculous infinity pool, dry sauna, wine cellar, yoga room and some of the sickest beach views you've ever seen in your life.

But TMZ has learned ... the bank recently foreclosed on the property because, according to official documents, KC's father Dennis failed to make payments on the $7,599,458.66 he owed on the place.

And now it's too late for the Cavallari's to get the place back ... because the house was sold at a public auction just last month for $6.1 mil.

Calls to Kristin's rep have not been returned.

It seems reality stars are getting knocked up left and right these days ... Snooki, Jessica Simpson, Kristin Cavallari, etc. ... but not Audrina Patridge ... at least judging from the way she looks in her bikini.

Congratulations.

Former "Hills" villain and half of one-time reality TV D-list supercouple Speidi ('memba them?), Spencer Pratt proved he's even larger now (left) than in his 2009 heyday (right) as he left a gas station in L.A. on Tuesday.

Look out K-Fed, because this is how Spencer rolls.

For a second it seemed to be 2009 all over again, as once famous famewhores Heidi Montag and Spencer Pratt (Speidi, anyone?) pretended to not know they were being photographed as they did something -- in this case, act all lovey dovey while skiing down a mountain -- on Thursday.

Seeing "The Hills" dynamic duo again makes one feel really thankful for the "Jersey Shore."

A production coordinator for "The Hills" claims she was unmercifully harassed sexually by a male staffer during the filming of the Costa Rica episode, and even "pressured" to smoke pot ... this according to a new lawsuit.

In the suit, obtained by TMZ, Eliza Sproul alleges Andres (she doesn't give a last name) -- a Costa Rican local -- was hired by MTV to do grunt work.  She says while they were driving together in 2010, she realized something was up when he took his shirt off and began making sexual advances, including comments such as, "I love your freckles.  I like your eyes.  Let's just take off."

A while later, Eliza says Andres drove her into the forest and "pressured" her to smoke marijuana.  We hate it when that happens.

Eliza has lots of other gripes, including:

-- She had to drive male cast members to a shoot and they were drunk and made crude and offensive jokes
-- She was forced to work insanely long hours
-- She had a meltdown and was abandoned in a hospital.
-- It got so bad doctors gave her Valium.

Sounds like a great trip to Costa Rica.

A rep for MTV declined to comment.

Spencer Pratt is telling friends he DOES NOT owe hundreds of thousands of dollars to his former agent, despite reports to the contrary ... because he's NEVER had an agent!!!

TMZ spoke with sources close to Pratt ... who tell us the couple worked with a lawyer when they were negotiating their deals for "The Hills" back in the day ... but they never involved an agency. We're told Spencer insists the lawyer was paid IN FULL.

We're told Spencer is now studying political science at USC ... and at the moment, he isn't actively pursuing work in Hollywood.

As for Heidi, one source told us she DOES have an agent -- whom she pays -- and she currently has "a couple of projects in the works."

Lauren Conrad is sooooooooooo over the Hollywood pad where she lived on "The Hills" -- and now you can own her leftovers for a cool $2.25 MILLION.

LC has listed her 3,009 square foot Spanish-style home -- which boasts 4 bedrooms, 4 baths, a pool, hardwood floors, a breakfast bar ... and a detached guest house where fellow "Hills" castmate Audrina Patridge used to live.

Seems Lauren will take a hit on the sale -- considering she bought the place in 2008 for $2.36 million.

Audrina Patridge and her mother Lynn showed off their hills & rockin' bods in matching teal green bikinis on the beach in Malibu on Wednesday.

Nothing beats a mother's love ... of her daughter's fame.