How do you call the gesture where you point at your head and make a circle or a few with your extended finger - when you want to imply someone, or some idea is "nutters" - something so ridiculous it's insane?
According to Wikipedia, this gesture is called:
Cuckoo sign, touched or screw loose. In North America, making a circling motion of the index finger at the ear or side of the head signifies that the person "has a screw loose," i.e. is speaking nonsense or is crazy.
I will repeat my warning that gestures are rooted in their cultural context and may mean completely different things in other cultures.