Warren Buffett isn't a fan of bitcoin. Not only does he think it's extremely speculative, but Buffett isn't a fan of most assets that don't do anything -- this is why you'll never see gold in Berkshire Hathaway's (NYSE:BRK-A) (NYSE:BRK-B) investment portfolio, either.

At Berkshire Hathaway's 2019 annual meeting, Buffett renewed his criticism about bitcoin and explained why it's not an investable asset.

Warren Buffett smiling.

Image source: The Motley Fool.

What Buffett has said about bitcoin and other cryptocurrencies in the past

Warren Buffett and Berkshire Hathaway's Vice Chairman Charlie Munger have both been quite critical of bitcoin in the past. At last year's shareholder meeting, Buffett called bitcoin "probably rat poison squared," and also said that he thinks cryptocurrencies won't end well for those who buy them. Munger added that trading in cryptocurrencies is "just dementia."

"In terms of cryptocurrencies, generally, I can say with almost certainty that they will come to a bad ending," Buffett also said in 2018.

Buffett's latest bitcoin comments

Warren Buffett's newest bitcoin comments seem even harsher. In an interview before Berkshire's annual meeting, Buffett called bitcoin "a gambling device" and also pointed out that there's been lots of fraudulent activity in the bitcoin world.

He also reiterated that bitcoin isn't a productive asset. That is, its value is based solely on the premise that someone else will eventually be willing to pay more for it. "It doesn't do anything. It just sits there. It's like a seashell or something, and that is not an investment to me," Buffett said.

Buffett compared bitcoin to a button on his jacket, saying, "I'll tear off a button here. What I'll have here is a little token. ... I'll offer it to you for $1,000, and I'll see if I can get the price up to $2,000 by the end of the day. ... But the button has one use and it's a very limited use."

In other words, bitcoin has limited real-world usability -- at least for the time being.

Should you avoid bitcoin altogether?

Obviously, don't expect Warren Buffett -- or Berkshire Hathaway, for that matter -- to buy bitcoin anytime soon. And from an investment standpoint, Buffett certainly makes some good points. It's really difficult to look at bitcoin's price action over the past few years and make a solid argument that owning bitcoin isn't highly speculative. Plus, Buffett has a pretty solid track record of pointing out irrational investment markets.

In short, while investing in bitcoin isn't a great way to allocate your investable assets in Buffett's view, that doesn't mean that you need to avoid it altogether. Just be realistic about your expectations -- if you put $100 on red on the roulette wheel at a casino, you know there's a substantial probability that you'll lose that entire $100. The same logic applies here. Investors shouldn't put any money into bitcoin that they aren't prepared to lose.