Tax question

BitcoinBitcoin
$21,012.65
‑9.45%
self.Bitcoin1m ago
Theoretically, let's say I acquired a bunch of bitcoin in 2012 thats now worth a whole lot. I find a Lamborghini dealer that takes bitcoin so I buy an Aventador. How do capital gains taxes work there? Does the dealer need to send something to the IRS? Am I realizing a gain when I exchange bitcoin for the car?