I know this must already be a thread, but I can’t find it. If it is, maybe someone can link.
Anyway, my guess is this list:
That leaves me one short. Did this episode (which recently reran) air before or after Sheldon met Prof. Proton?
I hesitate to include Bernadette, because Sheldon has specifically excluded Howard, so it seems odd that he would include Bernadette
Everyone else on the list he has specifically called a friend at some point, other than Beverly Hofstader and Stuart, although at a later date he will call Stuart a friend, and his weird intimacy with Beverly Hofstader, that Leonard knows nothing about seems to be his closest relationship on the show second to Amy.
Anyway, if I can include Prof. Proton, that’s nine.
Otherwise, could the ninth be his mother?