1) If you want a name like OpenGL_Guru, CodeGod, openglexpert, or bitchslapmaster (actual user names) - you must demonstrate that you have the competence in the area you are describing to live up to that name.
Though it would probably be best to trust that bitchslapmaster is actually a master of the bitch slap rather than find out. However, if I was a mod I probably wouldn't consider that to be an acceptable user name.
2) No names in all caps. Though some exceptions could be allowed - TANSTAAFL comes to mind as acceptable.