My mouth naturally turns down at the corners when I'm not smiling.
I have two all-too-frequent frown lines between my eyebrows, because bright light causes a glare that makes me unconsciously furrow my brows in an attempt to protect my eyes.
Apparently, I look angry most of the time. I'm not, actually. But I've had several people tell me that I look like it, when all I'm doing is just sitting there and being!