There is one for that! /scratch = "You scratch your head." I don't know how it works when it's directed at someone.
I second these suggestions. They would be soooo helpful.
Here are a few more ideas:
/sos - "You call for help." "You ask Person for help."
/thank - "You thank those around you." "You thank Person."
/forgive - "You forgive those around you." "You forgive Person." (Credit to @Kitty_Ironcraft)
/sneeze - "You sneeze." "You sneeze at Person."
/eyebrow - "You raise your eyebrows." "You raise your eyebrows at Person."
/trip - "You trip on a rock." "You trip Person."
By the way, this new emote is absolutely hilarious:
The directed functions seem to be working properly now, except for a slight problem with the /facepalm emote: