Resting bitch face. We've all heard the phrase . It refers to the facial expression of someone whose natural appearance seems, well, unapproachable. Specifically when she or he (yes, he, but more on that in a minute) is merely relaxing his or her face.This phenomenon of Resting Bitch Face, shorthand RBF, started off as an oblique insult for a woman whose stand-offish or annoyed look bothered those who thought she should be smiling instead. In other words, it was a ruse to tell a woman that she is being a bitch.That, however, is less true today. Jason Rogers, author of the study " Throwing Shade: The Science of Resting Bitch Face ," explained the reasoning behind the phrase, and his improved version, to Refinery29."Being called RBF may be a thinly veiled attempt to call someone mean, or even perpetuate benevolent sexist culture" he told us. "For example,'You’d be so pretty if you smiled more.'"Beyond the negative connotations of being a bitch, I'm personally indifferent to the comment. I myself have been told (numerous times) that I have #RBF. Enough so that I have been sent this more times than I can count. And, based on Rogers' Resting Bitch Face software, called FaceReader , the people who told me this aren't totally wrong. I sent my picture to him to see if my friends were right."I would not say you had RBF," Rogers told me via email, "but FaceReader is seeing the corner of mouth on the left side as pulled slightly." Basically he's saying that my natural face — the one I have when I'm commuting on the subway, waiting in line at Starbucks, or staring at my computer (ahem, right now) — is a face showing both "contempt" and a "neutral" expression.Here are 19 of the best celebrity Resting Bitch Faces, just so you know you're in good company. Own that RBF. It's the only F you've got.