My dear, never confuse efficiency with a liver complaint. — Mary Poppins

I don’t have a “resting bitch face”.  I have a “I’m tired and I’m ready to be left alone for a while” face.  Some take this as being unfriendly.  I take it as giving fair warning.

That being said, if I’m sitting there, looking like I don’t want to be messed with, and you have the manners to talk to me politely, it’s pretty good odds that I’ll break a smile, ask you to sit down, and enjoy some time with you.  Heck, if you’re at the house, I might feed you.  I just don’t advertise that service to the general public.

Of course, if I have that face, I’m backed into a corner, and I’m just staring at my cup or my food, it means I’m exhausted and really want to be left alone.  I can’t promise what happens then, but I do try to be at least polite.