Readers of my book may notice that I am fond of using.int as the TLD of preference for nonsensical example domain names. If you haven't noticed,.int is the TLD for international treaty organizations, like NATO, or arcane components of the UN. The.int registrar does not sell domains.
So I like to use "example.int" or the like, because I know that it's nearly inconceivable that any of my nonsense domains could ever become valid. I could use.gov, but.int is better.