Video of Paris Diaz Jordanou hamming it up for news crews has been viewed more than five million times since Thursday.
In the footage, Mr Jordanou is heard yelling "I'll catch him" as a car begins to float in floodwaters.
Social media users widely enjoyed his antics, with some joking he should be "Australian of the year".
But they were critical of the motorist, who escaped unharmed, amid warnings by authorities about driving through floods.
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Mr Jordanou told Nine's Today programme he was having coffee with friends nearby when they decided to go to the South Melbourne underpass, which is notorious for flooding.
He said he was "just being a larrikin (joker)" after becoming aware he was being filmed.
"It all happened organically - it was bit of a light bulb moment," he said.
"This time of year where there's a torrential downpour, somebody usually drives through there so we thought we'd come and have a look."
Despite laughing during the video, Mr Jordanou can also be heard trying to warn the driver to stop.
Victoria's State Emergency Service said 41 people were rescued from cars after the storm on Thursday, although not all deliberately drove into floods.
"Our advice is really strong not to drive, walk or play in floodwaters," a spokeswoman said.
"You're never sure what you're actually playing in. There could be debris that you can't see."
The emergency service received more than 2500 calls for assistance following the storm.
"This was a significant event that caused quite a bit of flash flooding to wide parts of Melbourne's greater area," the spokeswoman said.
An Australian man has found instant fame after being filmed pretending to fish during flash floods in Melbourne.