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Bitcoin has almost doubled in value since November, when commodities king Dennis Gartman last disparaged the cryptocurrency. Bitcoin's biggest bear still won't bite, though.
"Bitcoin on a volatile day moves 15 and 20 percent," Gartman said on CNBC's "Fast Money." "How can you margin something that can move 15 to 20 percent on a regular basis? It's the volatility that frightens me."
Volatility is a theme that routinely comes up in Gartman's rebukes of the cryptocurrency, which he maintains is a bubble waiting to pop.
"Bitcoin is the modern day Tulip Bulb mania. I will let others trade it, I won't trade it," Gartman said on CNBC's Fast Money.
Last month, Gartman told "Fast Money" the cryptocurrency "is a market ... for criminals, this is a market for millennials."
He softened his tone slightly Tuesday in light of the development that Cboe Global Markets will launch futures trading in the cryptocurrency beginning Sunday.
"It is gaining some sense of legitimacy by the Cboe," he said.
Still, Gartman maintained he doesn't think the cryptocurrency is out of the woods just yet.
"When they begin to pay taxes on it, when it ceases to be an avenue for avoiding taxes, when it ceases to be a place where drug dealers are trading and making transactions, then I'll be interested," Gartman said.