Mutumbo Finger
Infamous from Dikembe Mutombo, former NBA big man, waiving your pointer finger while saying, "No, no, no, no" he did this to opponents after blocking a shot. Similarly, doing so to people in public treats them as 3 year olds and makes them furious.
I cut off this erratic driver and passed him while giving him the Mutumbo finger, he punched his steering wheel in response.