“Oh. My. God. Becky, look at her butt. It is so BIG.”If you were of club dancing age in the past twenty years, then you’ve probably backed up your rump-o’-smooth-skin while shouting (from memory) Sir Mix-A-Lot’s notorious anthem to big butts and killer curves.While those butt-bashing opening lines—spoken by two skinny mean girls—have become a rallying cry for women of every size to stick out their butts and dance, many of us have probably been those mean girls at one time or another too.Unfortunately, criticizing other women’s bodies is par for the course among women. The practice even has its own term: body snarking.MORE: Are You a Fat Talker?“We think body snarking is the most common form of body talk,” says Denise Martz, Ph.D., professor of psychology at Appalachian State University. Women of all ages sneer at other women walking by (“She should not be wearing that”), at schoolmates or co-workers (“She totally has cankles”), at family members, celebrities, models—you name it.QUIZ: Do You Fat Talk ? Find Out for a Better Body Image.The media often fuels the fire and tabloid magazines have body snarking down to an art form. That is, if pictures of celebrities at the beach with a circle around their butts—Celebrities have cellulite? Gasp!—could even approximate art. But even the sweetest among us have been tempted by headlines like “Stars’ weight battles” or “Celebrities without makeup!”Today, we’re also taking those comments online, paving the way for even more aggressive body-bashing. “With the internet, we lose a bit of the interpersonal accountability that happens in face-to-face interactions,” says Martz. Imagine telling a girl to her face that, as one YouTube commenter wrote about Glee’s Ashley Fink, “there’s enough of her to provide sustenance for a village or two.” You’d never! But telling her in the YouTube comments thread? Less daunting.“Body snarking is bullying,” says Martz. Women tend to use words to build or break self-esteem, so teasing a girl about her body can have serious side effects, she warns. “One of the strongest predictors of developing an eating disorder is having been teased about one’s body by peers or family members. The impact can be devastating.”QUIZ: What’s Your Unique Body Type?If it’s so awful, why do we do it? Researchers aren’t sure yet, but they do have a few guesses. “We think it’s a way of creating an in-group versus an out-group,” says Martz. “Like the song, Baby Got Back, when the Caucasian women are discussing how big the African American’s butt is.” In other words, it strengthens social bonds and draws lines in the sand between separate social circles.Body snarkers may have selfish motives too. Martz suggests that it may make women feel better about their own bodies or distract them from self-critique in that moment. Still, that doesn’t explain why we put up with it when we know (and often lament) the pressures on women to look perfect. “It would be awful for men to critique women, but I struggle to understand why women critique their own kind,” says Martz.We’re always asking to see more “real bodies” in magazines or ad campaigns, so why are we so quick to criticize when we do see celebrities or real girls in all their flawed, airbrush-free glory? Ladies: It’s time to stop.Next time a girl walks in with an itty-bitty waist and a round thing in your face, why don’t you try telling her she looks great?MORE: Is Fat-Stigma Skewing Your Weight Perception?