A quick upward jerk of the head. An action that many teenage guys use as a greeting when they are too cool to say hello.
As Mary was walking down the hallway and saw her crush, she waved tentatively at him. He responded by giving her the chin-up
The act of texting only at a redlight by the person who is driving the car. Generally accepted as a safer way to text while driving because the driver is less likely to wreck, but they can still maintain communication with other people.
Mom: Kasey, put that phone away, don't you know you're not supposed to text while you're driving?!
Kasey: Mom, it's ok, I'm 18, haven't I at least earned the privilege of redlight texting? I'm not going to wreck.