Well, hang on, he does have a point. Bitcoin (and any coin which is yo-yo-ing right now) is not price-stable enough to be a true currency right now. You're right, you can use Bitcoin many places to buy something, today, at a lot of retailers, including a cup of joe. He's right in that why would anyone want to sell something (or buy something) when it's fluctuating in price so rapidly, literally in some cases by the minute? You can peg a crypto to fiat, that's no problem even down to the minute. You can easily say this is $1.25 in fiat, which when you walked in the door and got on line was 0.002BTC. By the time you get to the counter, the fiat <-> BTC rate has changed so that while it's still $1.25 in fiat, it's now 0.003BTC. You buy it, then it drops to 0.001BTC because of the market fluctuation, and now the vendor has taken a loss. What makes currency work is stability, low and predictable inflation / deflation, which changes over the course of a year, not 6 hours. This is why right now Cryptos are their own worst enemy. They aren't stable enough to be used as everyday currency (yet), but the fluctuate too rapidly which makes them look shaky, unstable, and frequently equated to penny stocks with the volatility and movement. It's easy to see why there's unease about it, if you look at it that way.