Girl Up, a new guide to life for teenage girls, starts as it means to go on: by saying "f*** that" to the sexist, know-your-place messages. "I didn't think there was any point in fighting fire with a spark," says its author, Laura Bates, best known for being the founder of the Everyday Sexism Project.

“This book has its own sexist bullshit klaxon,” she writes. “This book is the heroic, indomitable, slick it back, tie it up, don’t bother curling, who needs conditioner, any old elastic band will do, ponytail of books.”

This book is fabulous. It is inclusive and empowering. It is funny and frank and, as actor Emma Watson writes in the preface, "not for the faint-hearted". It is the kind of sex and life education you wished you had at your disposal when you were 14.

Conversations with young women over almost four years of visits to schools and universities taught Bates about “the sheer bombardment of crap they are putting up with – hypocrisy, double standards, body image pressure, sexting, online abuse, you name it,” she says.

And the advice that young women were getting was often inadequate for their lives. “It was things like, ‘Oh, just turn it off if you don’t like it’ or ‘Why do you need an Instagram account?’,” she says. “So much of what they were being told was either preachy or hopelessly patronising.”

Social currency

Girl Up sets out to "give them the social currency they need" to exist, and thrive, in the world they live in, as well as help to change it. From "new avenues for old forms of misogyny", such as sexting – which might mean unsolicited "dick pics" – to the perennial problem of street harassment, Bates offers a range of suggestions for how to deal with it, how to cope.

The title, “a little bit tongue-in-cheek”, plays on the phrase “man up” – an example, she says, of language that is casually damaging to both sexes.

“It suggests to girls that to get on with it, to deal with it, be brave, take matters into your own hands, to do it your own way, that those things are essentially manly, masculine things to do. And it suggests to men that there is something unmanly or wrong about showing emotion or being sensitive.”

An alternative title was Men Are from Earth, Women Are from Earth, inspired by the Mars-Venus dichotomy that is so stubbornly prevalent in popular culture, often among people who should know better.

“I think we enormously overestimate how much is biological and inherent in us,” says Bates.

We make ourselves miserable as a result. She discovered her “sexist bullshit klaxon” in March 2012 during a week of “little pin pricks” – being followed home by a man sexually propositioning her, being shouted at explicitly by a group of men on the street, being groped between her legs on the bus. Such incidents had happened before, but she had never done anything about them, “because it was part of being a woman”. She had normalised it.

Everyday sexism

A month later, to find out what other horrors were "normal", she set up the Everyday Sexism Project, a website to which people, men as well as women, could submit their stories. More than 100,000 contributions have been made so far, and in 2014, the book Everyday Sexism became the opening salvo in what looks set to be a long publishing career.

The submissions, still pouring in, come from all over the world. “They’re from a reverend in the Church of England being asked if there’s a man available to perform the ceremony, from a father being congratulated for babysitting his own children. They’re from a woman in India too afraid to report the man with the erection pressed into her back on the bus, from a woman in Mexico being told by her university professor ‘You look prettier when you shut up’. It’s just endless.”

What really annoyed her was the suggestion that this stuff wasn’t meant to be talked about. You were meant to stay silent about it.

“When women tried to speak out they were told ‘You’re overreacting. You’re making a fuss about nothing. Women are equal now. There’s no such thing as sexism any more. He meant it as a compliment. You just need to cheer up and smile, darling.’ ”

Being told to smile, often by strangers on the street, is certainly one of those bizarrely regular experiences common to most women, although it must surely have reached peak WTF-ness last month when the image of the slavery abolitionist Harriet Tubman, the new face of $20 bills in the US, was criticised for being too "stern". One hundred years after her death, a woman was being told to smile.

“That’s a good example of the kind of thing that people say ‘It’s no big deal’,” says Bates. “But it’s only when we call it out, and talk about it, that we recognise how absurd it is.”

Bates believes in a “spectrum” in which awful, “everyday” things – innocuous to some – are connected to the even more terrible, illegal things. The woman who is told she must wear high heels to work, for example, is suffering a version of the same attitude as the woman who suffers pregnancy-related discrimination at work.

“The same idea that women are decorative in the workplace,” she says, “is kind of connected to the idea that women have a particular function in society and that function is to have children.”

Girl Up explores careers – in a chapter called "Don't be shy, aim high" – but the main thrust of the book runs from body image ("You aren't your body") to the influence of online porn on ideas of how sex should be. Bates is open and nonjudgmental, but unafraid to identify harmful elements of our culture where she sees them.

One chapter is devoted to talking about the vagina, the vulva and the clitoris. Using the real words is important, she says, given slang terms such as “sheath” and “cock socket” imply that the vagina is merely a receptacle for a man’s penis, while other euphemisms, such as “gash” or “axe wound”, are grimly suggestive of sexual violence.

Sadly, it almost goes without saying that she has been personally on the receipt of death threats and rape threats.

I tell Bates I feel disheartened. Although social media has been great for feminism and the promotion of solidarity in so many ways – and Everyday Sexism is one of those ways – the body image pressure on young girls seems to be getting worse, not better. There are news reports about schoolgirls being told their bodies are “distracting” male staff by people who don’t seem to realise how that sounds. It feels like we are regressing on some issues, and we have barely even begun to acknowledge others, such as the impact of male violence on all of our freedoms.

In Ireland, women are denied basic healthcare and told it is immoral to seek their reproductive rights. We may feel cowed by the expectations upon us to be polite, not angry; quiet, not “shrill”; to play underpaid supporting roles.

Up for the fight

Bates, who is 29, is not only up for the fight, she is very usefully pointing young girls towards the armour and tools they will need to survive while the battle continues with no end in sight.

It would be “great to fix the media”, solve the problem of “inherently misogynistic” forms of porn and end the dehumanising of women in consumer culture, she says. “In reality, while I do think it is important to campaign on that, I don’t think it’s going to completely dry up and go away any time soon.”

Girl Up contains emoji, references to One Direction and an anecdote about Ed Sheeran, but it is Bates's willingness to be personal and confessional that shows most how in tune she is with today's no-barriers culture.

To demonstrate the “massive lie” and shifting goalposts of modern media images, she sends a picture of herself in a bikini to an airbrushing artist and publishes the before-and-after. She had been perfectly happy with the original, she writes, until she saw the airbrushed version. “It’s only when you compare the two that it makes the second one look ‘worse’.”

Jobbing actor

She grew up in Hackney in London before moving to Taunton in southwest England. When she moved back to London in her early 20s, she was a jobbing actor, but the casting breakdowns for the roles she auditioned for tended to be somewhat sketchier than the motivation-rich ones sent to her actor boyfriend (now husband).

“I would get ‘32DD’,” she says. “Or ‘she’s a vixen, but virginal’, ‘she’s naive, but fuckable’, or ‘she’s gorgeous, but in a nonthreatening kind of way’. Things that made you wonder if the people writing them had ever met a woman in their lives.”

Eventually, after so many of these dispiriting casting calls, she decided that acting and feminist activism could no longer coexist in her life.

She also shares with readers the experience of being dumped by a boyfriend for not being amused by his sexist jokes. “That was a genuine reason – among other reasons, to be fair to him, there was a variety of complaints. But one of them was genuinely that I couldn’t take a sexist joke.”

Did he see them as sexist jokes, or were they just jokes to him?

“I think he recognised that they were sexist, but thought it was just banter and that I was uptight,” she says. “It’s funny, because at the time I would never have used the word ‘feminist’.”

In Girl Up, she likens her feminist awakening to the experience of watching a film in 3D: "Once you put on the special glasses, it suddenly jumps out at you, as real as day in all its Technicolour glory, and you can't believe you didn't see it before. Once you put on the glasses, you can't take them off."

Does she ever get exhausted and overwhelmed by it all?

“Yes, is the honest answer. I think it is really draining and incredibly hard to read these very traumatic stories coming in on a regular basis,” she says. But she also feels “very lucky” to hear “the good stories”, the stories where young girls discover Everyday Sexism and tell her they’re standing up to it, shouting back, identifying as feminists and no longer feeling quite so alone.

• Girl Up is published by Simon & Schuster