I can’t tell if Weiss is partially smiling in a really horny way, or if she’s pissed beyond all belief and is trying to keep the rage in. Also, did anyone else notice that the three of them have her glyph symbol. She literally marked them as her property.

ZRT said:

I can’t tell if Weiss is partially smiling in a really horny way, or if she’s pissed beyond all belief and is trying to keep the rage in.

Weiss is pissed. You can tell by the cross-shaped anger vein on her cheek, it's a very common shorthand in anime.