The act of hitting the silent/reject/ignore button when some one is calling you on your cell phone that you don't want to talk to. You are essentially telling them "F you" hence it is called hitting the F you button.
This action may also be known as call dodging or a polite hangup
My dad was calling to gripe at me so I hit the F you button.
When my phone rang and I saw on the caller ID it was that ugly girl from down the street I had to hit F you button.