You wouldn't even need to take Bitcoin someone has access to.
There's tons of Bitcoin and other cryptocurrencies that are theoretically unrecoverable because the private keys to the wallets containing them have been lost, or the hard drives they were on were sent to a landfill (and thus began the world's shittiest treasure hunt).
However, by spending any of that Bitcoin you'd probably make international headlines and end up starting a market panic, because the most likely explanation for gaining access to that Bitcoin is that you found and exploited some vulnerability in the protocol itself.