Luann de Lesseps Flashes Butt While Doing Handstands in Mexico

Luann de Lesseps turned the shore of Mexico into her own personal gym ... performing acrobatics on the beach with the help of a pal -- and flashing her booty in the process.

Watch the video -- the reality TV star had a flipping fun time out on the sand during her recent vacation in Tulum ... putting her hands down and flicking her body up to playfully stand on her hands.

A man with her holds her legs -- so she's not exactly holding herself up like a circus performer. She did put on quite the show, though ... because when her cover-up fell down her body, it revealed her tiny bikini bottoms that left little to the imagination.

LdL's been living it up in the Mexico town recently ... packing on the PDA with her new boyfriend Michael Riemerschmid during a swim earlier this week.

The two locked lips in the clear blue water ... with de Lesseps later standing to reveal her teeny yellow two-piece bikini.