DeMario Jackson's Ex Puts a Bow on Her Assets!!!

Lexi Thexton's message to DeMario Jackson for ditching her to go on "The Bachelorette?" -- the pose says it all ... ya assed out on getting this!!!

Lexi showed off her buns in a pink bikini in Santa Monica ... and she's as hot as the sand.

You'll recall Rachel Lindsay infamously booted DeMario when Lexi made a surprise 'Bachelorette' appearance to confront him for going on the show even though, according to her, they were still an item.