The first thing Mark Cuban did when he became a billionaire was a "little naked billionaire dance."
Then he bought a plane, he tells the audience at OZY Fest in New York City.
Cuban became a billionaire back in 1998. That's when he and Todd Wagner took their online audio streaming company, Broadcast.com, public.
"Obviously I knew exactly what the number was to become a billionaire," Cuban says of the stock price, to the audience at OZY Fest.
"And so I am sitting there naked one morning. Naked. Bam, bam, bam, refresh, refresh," says Cuban. He was repeatedly hitting "return" on the keyboard to update the website where he was watching the stock.
"[The price] gets up there — and then I did my little naked billionaire dance."
He jokes that becoming a billionaire affected his appearance, too. "I was so much more handsome that next day. No lie," says Cuban.
Cuban's co-founder, Wagner, also became a billionaire with Broadcast.com.
"I'd put all my money into Broadcast.com — all my savings, all my 401(k)," Wagner tells CNBC Make It. "I had gotten a line of credit before I quit the law firm because I knew once I quit I'd never get a line of credit. I put all that in.
"So I went from somebody that had zero net worth to being on the Forbes [richest] list in six years."
Wagner and Cuban would go on to sell Broadcast.com to Yahoo for $5.7 billion in April 2000.
But both Cuban, 58, and Wagner, 56, grew up in working class towns. Cuban is from Pittsburgh. His dad upholstered cars for a living and his mom did odd jobs. Wagner is from Gary, Ind.
Coming into wealth suddenly is life-changing, says Wagner.
"You've won the lottery. There's no other way to really describe it. You can walk in a store and instead of saying, 'How much is that suit?' you can buy all the suits," says Wagner. "The first year, of course, you're happy every day."
In the long run, though, being a billionaire does not guarantee happiness, says Cuban.
"When I was broke, sleeping on the floor, starving — literally we would go anywhere that would give free food if you bought one beer, and I gained like 50 pounds," says Cuban of his early 20s. "I was broke, fat but having fun.
"And then when I made all the money, my wallet changed, my bank account has changed, but my approach to having fun hasn't changed," he says.
"People always say, 'What is your definition of success?'" says Cuban. "If you can wake up in the morning with a big old smile on your face, excited about the day, you are successful, and how much money you have doesn't change any of that. That is just who you are."
Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank," which features Mark Cuban as a judge.
Like this story? Like CNBC Make It on Facebook.