The index finger is usually placed between the eyebrows and wiggles awkwardly whilst saying, "Awkward narwhal..."
The middle finger is occasionally used, when an awkward moment is reached and the instigator of the awkward moment is acting douche-y and possibly insensitive to a prior occurence that makes the situation awkward.
Person 2: um, nothing.
Person 1: how's the girl?
Person 2: she dumped me.
Person 1: well how's basketball going for you?
Person 2: I didn't even make JV this year.
Person 1: oh. awkward narwhal.