A proclamation of sexual attraction. A hand resting on the knee. A flirty text message.
From the right person at the right time, they can make you feel great.
But from the wrong person or at the wrong time, an innuendo-laden text becomes creepy and an unwanted touch can make you feel uncomfortable and ashamed.
As the number of women making claims against Hollywood film producer Harvey Weinstein grows by the day, women around the world have spoken on social media about their experiences of sexual harassment under the #metoo Twitter hashtag.
Weinstein wielded great power, able to make or break his alleged victims' careers, but harassment can be just as damaging away from work.
In a global debate, the question of how we define sexual harassment is not altogether clear.
And that line between flirtation and harassment is a very fine - and often blurred - one.
So how do you ensure you stay on the right side of it? If you want to meet someone, you have to flirt, says relationship expert James Preece.
But it's about doing it in the right environment, not when people are least expecting it, he says.
He advises his clients - men and women aged from 23 to 72 - to play it safe by flirting in a playful - not a sexual - way.
"Be friendly and build up a rapport and trust," he says. At the end of the first date, he suggests a friendly hug or peck on the cheek.
When does flirting become sexual harassment? When it's unwanted and persistent, says Sarah King, of Stuart Miller Solicitors.
Dating expert James believes it's when a man goes too far - whether through what he says or what he does - when a woman clearly doesn't want it.
Sea Ming Pak, who goes into London schools to teach young people about sex and relationships, reels off a long list of what she thinks constitutes sexual harassment: non-consensual touching; feeling entitled to someone else; talking in a certain way; chasing girls down the street in order to chat them up; wolf-whistling and using a position of power or trust to talk in a creepy way.
The Oxford English Dictionary defines sexual harassment as "unwanted sexual advances, obscene remarks, etc".
Is sexual harassment illegal?
Not specifically. It is not a criminal offence in its own right, says Sarah King.
However, the types of behaviour that amount to sexual harassment can be criminalised under different pieces of legislation. For example:
Unwanted phone calls and messages, visits to home or work, taking personal photographs, unwanted advances and persistent and distressing comments
Sending indecent, offensive or threatening letter, emails, and messages on social media and text
Unwanted touching by someone who is getting sexual gratification, for example on public transport
More than half of women say they have been sexually harassed at work, according to research carried out last year by the TUC.
Why is sexual harassment happening?
Sea Ming Pak, who works for sexual health charity Brook, blames Western society's sex-sells culture which, she says, breeds entitlement and a blame culture.
Young people have been conditioned through films, music videos, TV programmes, access to porn and the normalisation of sending sexual images on phones, she says.
In school assemblies and classrooms, she tells them when it comes to sex you have to have freedom and the capacity to make the choice.
But she admits she worries about how poorly informed our schoolchildren are - with many blaming the victim when a rape scenario is presented.
In some cases, it is a learned behaviour, picked up from those closest to them.
She describes spotting a girl from one of her classes at a bus stop with a boy draping his arm around her and being "handsy".
"She did not look like she wanted the attention so the next week I told her: 'You have the right to say no, it was not OK for him to touch you.'
"I explained consent, and she replied: 'But they always grab me.'"
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