Kim Kardashian started an ass-selfie trend ... 'cause after she shared her bikini-wedgie with the world ... ANOTHER wanna-butt celeb is following suit.
This time, the chick showing off her donk is Mercedes "MJ" Javid from "Shahs of Sunset."
It's definitely a change of pace from Kim ... and pro surfer Anastasia Ashley, who beat MJ to the punch with a butt-selfie last week.
Butt-selfies -- sometimes they're not all they're cracked up to be.
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