A finger that's typically used to tell people to go
to hell and/or to fuck themselves by being positioned
upright while the other fingers are facing down inside the
palm of the hand.
I don't regard the middle finger as a negative physical gesture; whenever someone flicks me off I always assume they're conveying, "Excuse me
kind sir, but I'd like to introduce you to the pleasures of
prostate massage." To which I respond, "
Why thank you considerate stranger, I gratefully accept your generous offer; please lead the way so we may begin to experiment."