If you want a tag focused specifically on the face, then I must ask: how can you tell, looking only at the face and with no other context, whether an expression is horny or not? The only things notable about the face in this image are the blush and half-closed_eyes, neither of which are exclusive to aroused faces.
It's bad enough that we already have the context-dependent seductive_smile tag, which is nearly always indistinguishable from an ordinary smile. We don't need another tag that that has the same problem.
