It was an email like many she had had before: a lecture from a stranger explaining why her views - in his eyes - were wrong, all delivered hiding behind the phrase "dear sister, I say these things with greatest certitude of your Islam".
But this time, Egyptian-American journalist Mona Eltahawy was not going to ignore it. This time, she took to Twitter to express her frustration.
"Save your lectures, whether you're a total stranger or someone I know. 'Sister Mona' is not interested," she wrote, before asking others to share their story using the hashtag "Dear Sister".
Within hours, it had inspired thousands of tweets, with women from Australia to Pakistan, South Africa to Canada sharing their experience of being lectured to by men.
"To be honest, when I first tweeted it out, I did it almost as a joke," Ms Eltahawy told the BBC. The email - for no particular reason - had been the last straw.
But her flippant rant sparked a flame. Women flooded the social media site, revealing they too were fed up of being told how to dress and behave - much of the time by men who apply a double standard when it comes to their own lives.
Indeed, since her initial tweet on Sunday, the hashtag has been used more than 18,000 times, with many women sharing their own frustrations.
"I think what happened was other women looked and thought, it is not just me."
But as "awful" as many of the stories were, there was much to find strength in, said Ms Eltahawy, author of Headscarves and Hymens: Why the Middle East Needs a Sexual Revolution.
"I love the ferocity and energy," she said over the phone from New York. "It was not saying boo hoo [I am a victim], it was exposing the men."
Not that the men the tweets were talking about took it well. A common demand was to "stop talking about this stuff, you are making us look bad".
"My answer - and the answer of so many other Muslim women - was: we do not make you look bad. You make you look bad."
Of course, as Ms Eltahawy and many other women were keen to point out, their complaints did not include all Muslim men.
As one social media user noted, the #DearSister comments are "a reflection of culture, not Islam".
That did not stop the non-Muslim men who saw the tweets as "proof" of their Islamaphobic views telling the women to turn their back on their religion.
These women need neither thing, Ms Eltahawy says. "There is the internal right-wing, and the external right wing - and I reject entirely their messages."
But then there are the women who took issue with #DearSister - women Ms Eltahawy says have become the "patriarchy's foot soldiers", willing to accept the "crumbs" left behind by men.
"I don't want the crumbs - I want the cake," Ms Eltahawy said.
So, it seems, do many women on Twitter.
Ms Eltahawy hopes #DearSister could inspire more women to come forward and share their lives.
She dreams of holding readings, plays or putting together a book, collating their experiences.
"For me the most important thing it that #DearSister is a platform for Muslim women and girls - somewhere they get the space to speak, and everyone must listen."
Even if the book or readings do not come to fruition, you get the feeling she would be happy anyway.
"Muslim women all over the world are seeing each other," Ms Eltahawy says, clearly delighted.