Econo wave
Flipping someone the bird or giving someone the middle finger.
Econo as in economy, meaning thrifty management. Normally a wave utilizes all five fingers of the hand. In an econo wave, a person is conserving the number of fingers used in order to give someone just a one-fingered wave (i.e. the middle finger).
Britney: As I was driving down I-95, I saw one of those trash pickup crews on the side of the highway. I wanted to contribute to their effort, so I threw my Mickey D's bag out the window and onto the grass for them. One of the guys saw me and gave me the econo wave.