Not a tax expert and this is not tax advice, just my understanding:
A taxable event does not occur when the bitcoin comes into your account, any more than it would if you were depositing US dollars into a regular bank account.
The taxable event occurs when you dispose of the bitcoin for a gain. If you gave your friend bitcoin as a gift, for example, I don't think there was a gain. (Although there are limits on how much you can gift.)
If you sold it to him, then there was probably a gain (the difference between what you sold it for and what you paid for it). You only pay taxes on the gain. Re-purchasing the bitcoin would have no effect.
As far as I know, in the US, the gain is not considered a capital gain, its considered profit on the sale of property, so the rate is different (higher).
This assumes you already paid taxes on the money you used to acquire the bitcoin, but that is not the question you asked.
1Any thoughts on where you might use bitcoin through a payment provider to a retailer? If i use my dollars to buy a bitcoin at $200, it appreciates to $2,000 then I buy a sweet gaming rig for 1 BTC on Newegg. Do I just pay the sales tax on the purchase? Do I claim gains of $1,800 on my investment and pay taxes on that? Seems like a hazy area. – maple_shaft – 2017-06-26T19:37:21.263