I checked the default Avatar and it is “Mystery Man” (btw. in German WordPress this one is called “The pale gyu in front of a grey wall” ^^). I also changed the default, set the age rating for the Avatar to the highest rating but it did not make any difference.
Then I deactivated all other plugins just to make sure nothing overwrites the avatar settings but again, no difference.
What I noticed is that after changing the default avatar to ‘none’ and then setting up Super Socializer, your plugin seems to overwrite my default avatar setting with ‘Mystery Man’.