How about a 45mm? That ought to have enough punch to discourage road rage incidents.
From another thread ( http://www.freerepublic.com/focus/f-news/1718207/posts ), where a teacher got suspended for having a "toy gun [that] strongly resembled a 45 mm gun," I understand that they are small enough to put in your back pocket.
As long as the clip isn't in it, that is.
.38 spl smith and wesson w/ 3-4" barrel. Get a twin for you also. Simple to understand, ready when you need it.
BTW, if a "ladysmith" fits you both, don't let the name fool you. No one will call you a gillie man for carrying one. They have a smoother trigger pull straight from the factory. EVERYONE that has shot my wife's mdl 36 has fallen head over heels--serious macho types as well. It was a graduation gift from her Dad, and was his favorite among many. No, it's not as hi-capacity as an automatic---but when you grab it out in a pinch it's there for you one handed and RIGHT NOW!.
Also, many WWII guys will tell you that a victory model s&w revolver was a coveted teddy bear.