I know you were joking, but like everyone else I get tired of hearing this malarkey online and in every gun shop I frequent. They may turn and run..... or they may realize immediately where you are, that you're armed, and take the initiative to shoot first.
While not purely in the spirit of this thread, I'd personally prefer to go with a pistol-caliber carbine. Less noise and muzzle flash, and out of a carbine barrel most handgun rounds are a lot zippier. Perhaps this is where a 9mm Colt AR carbine would really be ideal.

