The term "girl car" should require no explanation.. but since this is here, I guess it still demands one.
It is, quite simply, a moniker given to a type of automobile that only those of the the female gender (or Gay Men) are given to operate. Another way of say this is "Self-Perpetuating Egotistical Male Machismo Bullshit". Because any "real" man drives a Ford Mustang or Land Rover, and you're not a Real Man(tm) unless you do. Riiight...
Such vehicles are given this distinction usually because of the style of the car, and sometimes of the power of the engine of the given car. But mostly it's on the body style -- especially if it is a convertable. The general synopsis of a 'girl car' mean any car that is smaller than a Midsize Sedan and isn't painted jet black (because it's a known fact that black paint cancels out all chick vibes).
Classic Examples (term used loosely) are the Volkswagen Cabrio, Golf and New Beetle, the Mazda Miata, Suzuki Swift/Geo Metro and the Toyota Tercel and Echo. What does this say to us? Well, my feelings are that this is trying to tell us that if you have a desire to drive a car that is small, looks nice and gets good gas mileage, my must be either a chick or queer.
Well, if digging guys is the price I have to pay to get a new VW Golf, well, fetch me my leather pants.