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Coutsos' avatars are often a Ninja'd version of something in the theme, while Cervantes' avatars are always Pirated (oh, oh, pun!).
Turns out alot of people type "Pythong" when they mean to type "Python" and somebody decided to take advantage of it.
What the Duck?
The first, and biggest, avatar theme was DuckFest.
The Baldur's Gate Revolution
In December 2005, Cervantes and Coutsos made Chuck Norris avatars.
Penny Arcade Violence
In January 2006, Cervantes and Coutsos made avatars involving violence in Penny Arcade.
Calvin and Hobbes
In February 2006, Hikaru79, Coutsos, and Cervantes made avatars of Calvin and Hobbes. Hikaru79 had a Calvin and Hobbes avatar for a long time, and had promised to partake in some of the previous avatar themes, though he never did. So, Cervantes and Coutsos brought this month's avatar theme to Hikaru79.
March 2006's avatar theme was actors or characters from movies.
To go along with the April Fools joke of 2006, some users (without their consent) changed their avatars to a Hello Kitty theme.