If you want a real fun gun for driving around or traveling, get a 4" Webley .455 (not shaved for 45acp). You can still find that Dominion Manstopper Ammo from the 40s around, packs a real punch (255gr@650fps) and is easy to shoot. Looks intimidating too.
Honestly tho, for non gun folks a S&W Model 10 is the ticket. 110gr 38spl +P in a carjackers face saves the US money in terms of trials, etc. Plus its not expensive so you dont cry when they seize it after you used it.
Dont forget the magic mantra: 'Yes Officer, all I wish to say now is that I reasonably believed my life was in danger and I acted in self defense to stop the threat. I want to contact my attorney"