"I just flipped a piece of cardboard for 3.6 million dollars in 24 months which required no manual labor," said Dave Oancea, who initially bought the card for $400K in 2018.

"That’s more money than each of my critics will ever make working a 9-5 for 40 hours a week for 40 years for a boss they don’t like even like."

The figure for the card is staggering ... it's now the most expensive baseball piece EVER -- smashing the $3.1 million record that a Honus Wagner card garnered in 2016.

Vegas Dave initially scooped up the Trout card because of its insane rarity -- it's a 1 of 1 -- and he guaranteed at the time the card would make him SERIOUS bank.

Ken Goldin -- whose Goldin Auctions company facilitated the sale -- told the Washington Post he wasn't exactly surprised to see VD's prediction come true.

"This [Trout] card is the best possible card of the best player today, and there’s only one of them that was produced," Goldin said. "And the whole world knows there’s only one.”

For the Angels' part, Trout's manager, Joe Maddon, was blown away by the sale ... joking with reporters over the weekend, "That puts him right up there with, what did the Mona Lisa sell for?"