LeAnn Rimes -- Back to Her Old THONG Habits

A rehabbed LeAnn Rimes got a fresh start to the new year ... by, once again, frolicking on the beach in a skimpy bikini for photographers in Mexico.

Just a few months after checking into rehab for stress and anxiety due to (according to her) the effects of social media ... the 30-year-old stepmother of two showed off her sexy slender physique in a thong two-piece swimsuit.

What better way is there to deal with the pressures of being judged on Facebook and Twitter ... than by showing off your womanly goods so everyone can Facebook and tweet about them?