The Spanish Finger is a gesture given to someone who has been NAUGHTY. It is equivalent to smirking while shaking one's head. To give the Spanish finger: lift your right arm, hold only your right index finger in the air, and move slightly right to left (this may be accompanied by a flirty smile if desired).
You are at a bar and a young, cocky but still cute international playboy comes up and tells you that he is taking you home later. Even though you are planning on going home with him as well, you give him The Spanish Finger to keep him on his toes. It is usually followed by a smart ass remark.
To get The Shaft (Definition 3) from someone, that is, to get screwed over. However - getting The Shaft is common enough - you realise you have received The Spanish Finger only after the fact. So, in (say) a review situation - your boss makes a couple of critical remarks that are so subtle you only realise it afterwards. That is The Spanish Finger. Realisation of having just received The Spanish Finger is normally accompanid by a puzzled frown and a rub of ones chin. This was first coined in Rathmines on December 9, 2005.
What a strange review that was. I almost feel as if my boss was being rather critical of me. (Pause) In fact he definitely was. I just received The Spanish Finger. Damn.