People are idiots. The first idiot thing you can expect is that they'll deny they are idiots and will insist that you shouldn't idiot-proof things.
The second is, since they're idiots, they'll hurt themselves on the things you didn't idiot proof.
The .int Top Level Domain has existed since the 1980s. Nevertheless plenty of people decided they'd use names ending in .int for "internal" stuff. Then they were astonished that this doesn't work as expected. We even had to smack CAs for issuing certificates for such "internal" names back when they were allowed to do that (today CAs trusted in the Web PKI are not allowed to issue for names that aren't part of the Internet DNS hierarchy with a narrow exception for the .onion pseudo TLD).
The second is, since they're idiots, they'll hurt themselves on the things you didn't idiot proof.
The .int Top Level Domain has existed since the 1980s. Nevertheless plenty of people decided they'd use names ending in .int for "internal" stuff. Then they were astonished that this doesn't work as expected. We even had to smack CAs for issuing certificates for such "internal" names back when they were allowed to do that (today CAs trusted in the Web PKI are not allowed to issue for names that aren't part of the Internet DNS hierarchy with a narrow exception for the .onion pseudo TLD).