It was 10 years ago, on the bus on my way to work, that I first saw a man using Grindr.
I had heard friends describe a free iPhone app that could show you where the nearest gay guy was. And sat in front of me was an early adopter, tapping his way through a grid of topless torsos and replying to a flurry of messages.
The concept was extraordinary.
When Grindr launched in March 2009, the iPhone was still in its infancy.
Back then, the BlackBerry was king. Apple's app store was less than a year old and there was no Instagram or Snapchat. There was also no Tinder or Scruff or Bumble, or any of the countless other location-based dating apps that Grindr paved the way for.
The app was created by Israeli entrepreneur Joel Simkhai as a way for gay men to make friends.
Gay hook-up websites such as Gaydar were already used by millions. But Grindr changed the game by using the iPhone's satellite location data to let people discover other men nearby.
Grindr quickly toppled Gaydar, which was slow to adapt its own app. Online dating and the future of the gay scene changed forever.
Today, Grindr says it has about four million daily users in about 200 countries.
"It's an Argos catalogue of gay men, in stock, ready for collection," says comedian Jack Rooke, who tells stories of his Grindr experiences as part of his stand-up.
As a young man, coming to terms with his sexuality, it also helped him connect with his peers.
"It was just good to speak to another gay human being," he says, describing the time he went to a man's house for a hook-up but ended up discussing life over homemade pitta bread and dips instead.
"Grindr was for me the place where I learned so much about gay culture and queer culture and what it means to be a gay person."
The app has its fair share of success stories. Great hook-ups, happy marriages.
But something about Grindr also drew out the worst in people. Stories about receiving unsolicited abusive messages, or arranging dates with men who did not show up, or sharing intimate photos with a fake profile soon spread online.
For most of its history, racist bios were common on Grindr dating profiles.
"You would see profiles saying no Asians, no blacks, no fat people," says Jack. "There's been a huge space for prejudice on that app, I think since day one."
Dating no-shows and racist messages spurred blogger Andrew Londyn to write a book describing how to "survive" Grindr.
He recalls chatting several times with a "very handsome Greek guy". Eventually the man asked why the pair had not met for a drink.
"You haven't asked me out yet," Andrew replied in jest. But the response was bleak: a tirade of racist abuse.
"That was infuriating. You just asked me out, and now that?" says Andrew.
On his blog, Andrew describes the loss of "community" he feels apps such as Grindr have contributed to. Previously men of all ages, backgrounds and body types would meet in bars and spend time together. But today, people can select their friends from the online catalogue instead.
"We're dehumanising each other," says Andrew.
"We don't think of it as an individual who is reaching out to me. They have a mother and a father, they probably have siblings, they work, they want to be happy. But we just view them as a picture. If you view them only as a picture, they're easily disposed of."
The arrival of Grindr and the rival apps it inspired brought a fresh challenge for LGBT venues, many of which have seen visitor numbers decline.
"Grindr was the next evolution along from the internet, as to how gay men started to meet each other and hook-up," says Mark Oakley, owner of the Eagle bar in London.
Ten years ago, his venue was renowned for its late night sex parties. A black curtain separated the bar from the "dark room", where anything could happen. On a Saturday you could "hear the spanking down at Vauxhall station".
But demand for that type of night out declined as Grindr's popularity grew.
"Grindr came along offering a much more direct route to sex with no real barriers. Why would people want to go to a club, pay a door entry fee, pay for drinks, when there might not even be anyone there they like?"
Mark accepts it was a natural progression for sex to move online, comparing it to the entertainment industry shift from CDs and DVDs to downloads and streaming.
"Businesses have had to shape up, or ship out.
"For us to survive in today's market we had to evolve and change in to what we've become now. We had a considerable refit, brought in a new look and feel. Now it's all about the music and entertainment."
The black curtain, he says, was ceremoniously discharged and recycled.
Grindr has at times been used for the worst imaginable crimes. In 2016, serial killer Stephen Port was jailed for killing four young men and raping four others. He used Grindr to set up his killings. And in 2018, Daryll Rowe was jailed for deliberately passing HIV on to several other men he met on Grindr.
Any new technology can be used for terrible purposes. But Mark fears Grindr has left a "wreckage" in its wake, by making it easier for lonely or isolated men to meet people offering drugs and chem-sex parties.
Officially, Grindr's community guidelines prohibit "mentions or photos of drugs and drug paraphernalia, including emoji" but that does not deter everyone.
Some profiles openly advertise HNH (high and horny) meet-ups. The diamond emoji is often used by people offering crystal meth. Grindr is not to blame for gay and bi men taking drugs, but it may have made it more accessible.
"Grindr has a social responsibility and it should take that seriously," says Mark.
"They put up messages, but they could do a lot more. The licensed trade has to control what happens on our premises. Why don't they?"
In January 2018, Grindr was fully acquired by China's Kunlun Group. It paid a total of $245m (£185m) for the platform, and creator Joel Simkhai left the company.
Since the publication of this article, the company told the BBC that privacy remained its "top priority" and all user data was stored in the United States.
One of the first changes after the acquisition was the launch of the Kindr Grindr campaign, designed to "address issues such as sexual racism, transphobia, and body shaming".
"Kindr is built on education, awareness, and specific policy changes in the Grindr app to promote healthier interactions among our users," the company told the BBC.
The app also changed its community guidelines. Now, anybody using racist or dehumanising language on their profiles can be banned if reported.
"We are also actively working to update our new user on-boarding experience, which will guide new members through their first steps of using Grindr, highlighting the importance of positive behaviour when communicating with others in our platform," the company said.
Looking ahead, Jack hopes Grindr will continue to evolve and tackle toxic behaviour.
"I hope Grindr becomes a tool for more good," he says, especially as some groups in the UK are "discussing whether or not we should teach LGBT education to young people".
Grindr told the BBC its priority would always be to help the LGBT community "connect and thrive".
"As part of our ten-year anniversary, we are placing a strong focus on authenticity. We want our users to have meaningful and authentic experiences. In the coming year, we will be rolling out new features, showcasing real stories of real users, getting involved in community events, and finding more ways to give back to the LGBT community," a spokeswoman said.
In the fast-paced world of apps and websites, market leaders can be quickly toppled. If Kunlun wants Grindr to stay ahead, it will need to do all it can to make its app a welcoming and desirable place for men to meet.
You can hear more from Jack and Andrew on the BBC's Beyond Today podcast later this week.