It's completely acceptable to use .local. in such a manner, however.
The "conflict resolution" process is outlined in the RFC [0] and is, well, pretty simple:
> ... the computer (or its human user) MUST cease using the name, and SHOULD attempt to allocate a new unique name for use on that link.
You can even set up your own DNS servers to be authoritative for the ".local." domain (zone), if you really want to.
RFC6762 states that "any DNS query for a name ending with '.local.' MUST be sent to" 224.0.0.251 (or ff02::fb) -- but it also explicitly allows sending them to your regular ol' (unicast) DNS servers, too. It's up to you to figure out how to manage that, of course.
Now, that said... to avoid any potential issues, I'd only ever use .local for its intended purpose. There's just too much potential for "weirdness" to occur. Personally, however, I completely avoid any use of either (.local and Multicast DNS) regardless.
--
On a side note, ".localdomain" mentioned in the grandparent comment should actually be "localhost."
Jokes aside, isn't this what .local and .localdomain are specified for?
Why not use nickname.local as your namespace?... it's probably unique enough at least on this planet.
Of course another way would be to register one gTLD for each person on the planet, which seems to be the trend as of late /s