That episode was far from the last. Years of verbal and physical sexual affronts left Mehra, now 29, filled with what she described as "impotent rage."
Last week, she and thousands of Indian women like her poured that anger into public demonstrations, reacting to news of the gang rape of another young woman who had moved to the city from a small village, with a new life in front of her.
That woman, a 23-year-old physiotherapy student, died Saturday from internal injuries inflicted with a metal rod during the rape, which took place on a bus two weeks ago.
In her story and its brutal ending, many women in the world's largest democracy say they see themselves.
"That girl could have been any one of us," said Sangeetha Saini, 44, who took her two teenage daughters to a candle-filled demonstration on Sunday in Delhi. Women in India "face harassment in public spaces, streets, on buses," she said. "We can only tackle this by becoming Durga," she added, referring to the female Hindu god who slays a demon.
Indian women have made impressive gains in recent years: maternal mortality rates have dropped, literacy rates and education levels have risen, and millions of women have joined the professional classes. But the women at the heart of the protest movement say it was born of their outraged realization that no matter how accomplished they become, or how hard they work, women here will never fully take part in the promise of a new and more prosperous India unless something fundamental about the culture changes.
Indeed, many women in India say they are still subject to regular harassment and assault during the day and are fearful of leaving their homes alone after dark. Now they are demanding that the government, and a police force that they say offers women little or no protection, do something about it.
Ankita Cheerakathil, 20, a student at St. Stephen's College who attended a protest on Thursday, remembered dreading the daily bus ride when she was in high school in the southern state of Kerala. Before she stepped outside her house, she recalled, she would scrutinize herself in a mirror, checking to see whether her blouse was too tight. At the bus stop, inevitably, men would zero in on the schoolgirls in their uniforms, some as young as 10, to leer and make cracks filled with sexual innuendo.
"This is not an isolated incident," Cheerakathil said of the death of the Delhi rape victim. "This is the story of every Indian woman."
While the Dec. 16 attack was extreme in its savagery, gang rapes of women have been happening with frightening regularity in recent months, particularly in northern India. Critics say the response from a mostly male police force is often inadequate at best.
Last week, an 18-year-old woman in Punjab state committed suicide by drinking poison after being raped by two men and then humiliated by male police officers, who made her describe her attack in detail several times, then tried to encourage her to marry one of her rapists. Dozens more gang rapes have been reported in the states of Haryana, Bihar and Uttar Pradesh in recent months.
The government does not keep statistics on gang rape, but overall, rapes increased 25 percent from 2006 to 2011. More than 600 rapes were reported in New Delhi alone in 2012. So far, only one attack has resulted in a conviction.
Sociologists and crime experts say the attacks are the result of deeply entrenched misogynistic attitudes and the rising visibility of women, underpinned by long-term demographic trends in India.
Thanks to years of aborting female foetuses, a practice that is still on the rise in some areas because of a cultural preference for male children, India has about 15 million "extra" men between the ages of 15 and 35, the range when men are most likely to commit crimes. By 2020, those "extra" men will have doubled to 30 million.
"There is a strong correlation between masculinized sex ratios and higher rates of violent crime against women," said Valerie M. Hudson, a co-author of "Bare Branches: The Security Implications of Asia's Surplus Male Population." Men who do not have wives and families often gather in packs, Hudson argues, and then commit more gruesome and violent crimes than they would on their own.
Others point to the gains that women have made as triggers for an increase in violent crimes.
"Women are rising in society and fighting for equal space, and these crimes are almost like a backlash," said Vijay Raghavan, chairman of the Centre for Criminology and Justice at the Tata Institute of Social Sciences in Mumbai. If poverty and unemployment were the only reason for these crimes, rates would already be much higher, he said, because both are constants in India.
In India's conservative society, male sexual aggression is portrayed in unexpected ways. In Bollywood films, kissing on screen is still rare and nudity forbidden. But the rape or harassment scene has been a staple for decades, usually featuring an innocent woman who resists nobly, but eventually succumbs to sustained pressure from the male hero. One commonly used term for sexual harassment is "Eve-teasing," which critics say implies the act is gentle and harmless.
The New Delhi rape victim, whose funeral was held on Sunday, and whose name had not been revealed, was from a small village in Uttar Pradesh, India's most populous state. Her journey to Delhi was the same that thousands of young women make every year to big cities around the country, in search of a better education and opportunities than their parents had. "My brother's entire salary was spent on educating his children so that their aspirations were fulfilled," the woman's uncle told The Hindu newspaper.
In South Delhi, hundreds of students from Jawaharlal Nehru University organized a silent march from their campus to Munirka, the bus stop where the rape victim was picked up, after her death became public on Saturday. The crowd of protesters trudged along a busy road, a few holding hastily made placards with phrases like "You are an inspiration to us all."
"There's a movement that has been built out of this," said Ruchira Sen, 25, a student of economics on the march to Munirka. "We are going to do everything it takes to make it last," she said.
Students and activist groups have presented a list of demands to the government, including the fast-tracking of rape cases through India's courts and improved training for the police.
Part of the policing problem is that less than 4 percent of India's overall force is female, said Suman Nalwa, head of Delhi's special unit for women, in an interview. She said she was working to improve police response to sexual assault.
"Earlier, women didn't leave their homes, so there was no crime," Nalwa said. "We are doing our best, but, of course, there is a lot more to be done."
Like many who attended these protests and rallies, Mehra had been urged to go by her mother, who she said had given this reason: "Because I don't want my granddaughter to face this."
Men have also been a large presence at the protests, though not always a positive one. After the large central Delhi protests on Dec. 22 and 23, the police received 42 complaints from women about men's behavior there, said a senior police officer who spoke on the condition of anonymity because the information was not public. He balked at describing the actions as "harassment" or "molestation," saying that implied aggravated or sustained behavior. Instead, he said, the men were merely "Eve-teasing."