I've had a few people ask why I use the screenname "Grognard" (and grognard66 on other sites). My roots are in wargaming - originally board games (Avalon Hill) and, subsequently, computer wargames (SSI/Talonsoft).
That community affectionately adopted the term "Grognard" as a tongue in cheek way of acknowledging how grumpy they could be if even the most trivial details (ballistics, etc.) were not precisely correct in a game. This is a reference to Napoleon's Old Guard troops who were widely acknowledged as the best soldiers (I know it's hard to imagine - good French fighters!), but had a reputation for constantly complaining - so "Grognard" means grumbler. Anyone who follows my comments and posts knows that I can be grumpy on occassion. 
The "66" is simply my year of birth. So there you go - your history lesson for the day!