... Take It From a Rich Guy Like Me!!!

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Barstool Sports honcho Dave Portnoy feels like a million bucks (way more, actually) ... which explains why he's dishing free advice on prop bets for Super Bowl LIV.

Portnoy joined "TMZ Live" Thursday from Miami -- site of Sunday's Super Bowl -- and dude had a million reasons to smile -- more like 450 million reasons, actually, after selling a 36% stake of his media company worth $163 million in stock and cash. The sale bumped the valuation of Barstool's digital media brand to a whopping $450 million.

El Presidente -- as he's referred to by Stoolies -- tells us how he's gloating in South Beach, and ya can't blame him. He also gave us quick advice on this year's prop bets ... such as, the over/under on how long Demi Lovato's national anthem song will last and whether J Lo or Shakira -- co-headliners of the halftime show -- will have a wardrobe malfunction.

TBH, Portnoy's answers make a ton of sense.

As for whether he'll be at the big game, that's unclear -- seems Dave is still on the NFL's bad side after he used a fake mustache to sneak by NFL security at last year's Super Bowl.