A meme from Tumblr page KushandWizdom explains why the phrase "act like a girl" can be so damaging to young women, as well as why we ought to stop saying it:

KushandWizdom - tumblr.com

The saying "act like a girl" reinforces gender stereotypes that are very limiting for men and women alike. When you tell someone to "act like a girl" or behave in a "ladylike" manner, you are commanding her to subscribe to female stereotypes and potentially hindering her true self. It implies that there are certain behavior constructs that are specifically feminine—and in some cases "girl" like behavior is seen as "weak." These gendered phrases also imply that men should avoid certain behaviors.

Growing up, I was told that I was not acting "ladylike" enough. I ate my meals too eagerly, laughed too loudly, burped in front of the wrong people, and seemed "unbecoming" when I occasionally swore. While the criticism initially lowered my self-esteem, I eventually took issue with the notion that males and females are supposed to carry themselves in a gender specific way.

Last year, feminine products company Always addressed negative gender stereotypes in its viral #LikeAGirl ad campaign. In the video below, several adults and little girls are asked about what it means to do certain activities "like a girl." While some of the adults fight in a silly, catlike manner when asked to "fight like a girl," the little girls exhibit strength and toughness during the same exercise.

In the video, a little girl is conflicted when asked whether "like a girl" is a good or bad thing.

"I actually don't know what it really ... if it's a bad thing or a good thing," the girl says. "It sounds like a bad thing. It sounds like you're trying to humiliate someone."

"Like a girl" and "ladylike" aren't the only phrases that perpetuate gender stereotypes. Last month, ATTN:'s Mackensie Graham wrote that "man up" can be very damaging to men.

"From a young age many boys (and girls) are told to match their behavior to constructs placed on their gender," she wrote. "This idea of 'man up' in a simple term carries a multitude of prescribed musts that a man should be: strong, stoic, powerful, unyielding. All of these terms are valid in their own right, but as a construct tied to masculinity and encouraged for all genders is unnatural."