I am fine at reading facial expressions if they are on smilies.
But I mix them up on people because while a smiley obviously has an upturned mouth when grinning, some people don't and they look more like their baring their teeth, or in other words, angry.
I don't think I have any deficits in understanding changes in voice tones and stuff... that's why I don't have any troubles comprehending sarcasm.
Gestures are my worst nightmare, though... the only ones I understand are pointing, waving, shrugging shoulders and sighing (the latter two I learnt from books
)
Gestures confuse me...I rarely use them. Really I pretty much never use them. And they are distracting to me if someone uses them. I usually can't read facial expressions because I rarely look at people but if I really try I can sometimes figure out what they mean.