Ha, absolutely footle - case in point! 
Wrt nn, potato you might not see the need to shorten or abbreviate but a Lot of kids do - most of my friends throughout school were known by their one syllable nn.... In some cases the parents Hated it but what could they do?! 
It's not a bad idea to have your own nn on the back burner - saves someone else thinking up a less favourable one at least!