example.com is also always a safe one; RFC-2606 defines four top-level domains and three second-level domain names permanently reserved by IANA for testing purposes: .test, .example, .invalid, .localhost, .example.com, .example.net, and .example.org.
> This is why I use foo TLDs in the documentation. To make sure it won't work in a copy-paste situation
You're describing the exact methodology that led to this problem.