give sb the finger 對人比中指

定義
to show someone in an offensive way {that you are angry with them by [turning the back of your hand towards them ]and [putting your middle finger up] }對他人表達你的憤怒不爽的一種侮辱攻擊方式

an offensive way 一種侮辱攻擊方式
putting your middle finger up 舉中指

thumb a lift 想搭便車(就舉姆指)
to stand near the edge of a road and hold out your hand with the thumb raised as a signal for a vehicle to stop and take you somewhere:

例如: We thumbed a lift to London.