When I had my Stealth, I noticed that the flat strip in the back was teh exact size of your standard LED Marquee panel you see in some businesses. Mount that in there, a few pre-recorded macros and a keyboard...
\"You drive like old people ★■◆●. Slow and sloppy\"
The only problem I see with using this would be the ★■◆● behind you when you turn it on to call him stupid and he'd follow you till you stop, come out, and shoot you.
I dont think such \"you are teh suck driver\" messages will matter anyway since many people are so oblivious while driving. Its kinda hard to communicate with people when they only have 2 brain cells working, sometimes not at the same time.