put two fingers up at somebody

Từ điển Oxford Advanced Learner 8th

put/stick two ˈfingers up at sb idiom
(BrE, informal)to form the shape of a V with the two fingers nearest your thumb and raise your hand in the air with the back part of it facing sb, done to be rude to them or to show them that you are angry
see also ↑V-sign
•She enjoys sticking two fingers up to convention.
Main entry: ↑finger_idiom