Quickie suggestions:
"Honk if Someone in Your Car is an N"
"Narc Drop-Off Vehicle"
"Psychopath
GPS
on Board"
"N/P Survivor.
If You Hit Me I'll Survive That Too.
Will You?"
"What? Too Entitled to Sit in Traffic?"
"Honk if You've Stolen the Car You're Driving"
"I Can See the Body Parts
in Your Tire Treads."
(OK, so this one is a little out there -- I'm channeling NCIS.)
"How Many Psychopaths
are Driving Next to You Right Now?"
"Do You REALLY Know What Motivates
the Driver Behind You Right Now?"
"Triangulating
N/P
Drivers Right Now"
NewWings4MeNow