5 minutes later they disappear and you're left wondering why you didn't just say hello and fantasising about what could have been and hoping one day you'll meet again.
Thankfully, this is the 21st century and now there is an app that allows you to turn back time, kinda, and reconnect with that person through the powers of your smartphone.
Happn is the latest dating app to take over the nation, designed to help you discover the people you have crossed paths with and that you would like to find again. And with over 4 billion users the chances of this happning are pretty high.
The app is 'geolocated' and uses real-time: every time you cross paths with another member - whether you're in the street, in the club or at a party - their profile immediately appears on your app.
As someone who is a little wary of dating apps replacing real life communication it comes as a comfort to me that, unlike it's rivals, Happn believes in 'the now' and is there to encourage you to make the first move and approach someone in real life, rather than becoming a tool for the real you to hide behind.
People may have their qualms about online dating, but speaking from experience it really is a great way to meet new people, whether you end up wan't to pursue it romantically or not. And going on dates is always a laugh, particularly afterwards when you get to dissect the evening, relaying every detail back to your mates.
So go on all you singletons, just watch as the matches roll in and maybe, like I did, you'll actually find someone worth sticking with.