There are a few facial expressions. Exasperation, Anger, Laughter, and AFK. It would be really really nice if I could just give another glitch a friendly smile as well.
For the sake of those who don't know, you can press the number keys while playing to do a few basic emotes, that very a bit from face to face. But as a general guide:
1 - O.o (same as using purple flowers)
2 - angry face
3 - smile/laugh
4 - enters you into AFK mode (sleeping)
I use laugh :) when I want to smile but... I agree, sometimes the all out laugh is socially awkward. Like I'm demented and laughing randomly across from someone while mining sparkly.... my preciousssss.