I can't find the exact frame, but it's in this scene in WW:
A second before Link makes this face, Link is seen, for a breif moment making a smug "man, this thing is bad ass" face. This is right after he pulls out the Master Sword for the first time and gives it a few test swings. He looks at the sword, smirks slyly, shakes his head as if to say "I can't believe I'm even holding this thing," and slants his eyes. Then, after that half second of indulging in the coolness of the moment, he goes to this pose, where he remembers his duty and remains humble in the presence of the blade of evils bane.
Not only is this by far the most effective Master Sword moment in any Zelda game because of it's subtleties, but it is by far my favorite gaming moment of all time, because for that split second, Link and the player are completely and flawlessly in sync.
