'Shark Tank' star Kevin O'Leary has an unusual splurge: $120 luxury underwear

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Everyone has something they're willing to splurge for — even the cast of ABC's "Shark Tank."

Barbara Corcoran indulges in fresh flowers and trips with her girlfriends. Robert Herjavec is always willing to shell out cash for valet parking. Mark Cuban splurged on a private plane.

But for "Shark Tank" star Kevin O'Leary, the luxury item on which he's willing to spend a pretty penny is certainly unique.

"My underwear cost $120 each," O'Leary tells CNBC Make It.

O'Leary says he buys his boxers from Zimmerli of Switzerland, a company that has been hand crafting underwear since 1871.

"They're made from Egyptian cotton," O'Leary says. "I love them."

O'Leary also admits to getting $80 haircuts.

"I don't have that many, so I want them to have a personal relationship with every hair," he says.

It's all about looking and feeling his best.

"I invest in looking great all the time, and the way I do it is [paying for] great clothing, great shoes and a haircut every 10 days," he explains.

However, there are some things he refuses to spend money on.

"Do I pay $2.50 for a coffee? Never, never, never do I do that," O'Leary tells CNBC Make It. "That is such a waste of money for something that costs 20 cents. I never buy a frape-latte-blah-blah-blah-woof-woof-woof for $2.50."

Why Kevin O'Leary refuses to spend his money on fancy coffees

O'Leary's personal finance philosophy is to avoid buying frivolous things, then invest the money you're saving.

"The truth is, there is a lot of crap you don't need," he explains. "What I've learned to do, and what has really helped me in maintaining growth in my own personal investing is, anytime I pick up something I'm going to buy, I say to myself, 'Do I really need this?'

"Because if I don't buy it, the money is going to be invested and make money every year for me while I'm sleeping."

And if you do want to splurge, check in on your budget first, O'Leary says. As a multimillionaire, the shark can afford his expensive underwear.

"The biggest mistake in life people make is their lifestyle — their lavish lifestyle is more than they are actually making," he says. "The best thing would be actually to only spend 90 percent of what you bring in, and invest the other 10 percent for the future."

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Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank."