the Futhank you wave

The act of raising your hand after making an aggressive and rude traffic faux-pas, like changing lanes 2 feet in front of someone because you were going to miss your offramp.

The Futhank you wave is both a thank you and yet can be issued with no sincerity whatsoever- hence the F.U. prefix.

I swear that guy I cut off was going to kill me until I gave him the futhank you wave