Nardone shouted and swore at Osmond before squaring up to him as if he was about to do something more, two former employees said.
In person, Nardone was hyper, ambitious, and volatile, our sources said.
He had the ability to charm investors and would-be employees, but several former staff said they ended up scared of him, citing his unpredictable moods and confrontational approach as major issues.
The new HQ was roughly 15 minutes walk from his riverside penthouse apartment at Distillery Wharf.
Fling was built in less than four months between March and July 2014.
Several of them said they believed Nardone's behavior changed significantly during Fling's lifetime, while others told stories of mysterious girls around the office and wild party weekends. After failing to secure the funding it needed to continue, Fling quietly shut down in August 2016, based on bankruptcy administration documents submitted to Companies House by Unii Limited.
Nardone told Business Insider he refutes what his former colleagues have told us, but he declined to comment further.
It narrowly missed and collided with a glass window above his head.
The event was described to Business Insider by four former employees.
But the entrepreneur said he had a flash of inspiration for Fling while on a flight to Hong Kong in January 2014, which ultimately led to the demise of the platform.
"While I was staring at the flightpath map on my seat screen I had one of those insane moments where my fingers couldn't type my idea fast enough on Notes," he told Tech Crunch. What if you could 'fling' a private message out to the world, and literally see it fly and land all over a world map – much like the one I was looking at on my British Airways seat screen.
The app — built by up to 50 staff and backed by a network of wealthy individuals from the UK, Italy, and Asia — struggled to retain users.