position, if you just go at it intelligently. You rock over on the weak side buttock, as your strong side hand goes towards strong side front pants pocket. You straighten-push down with strongside leg, raising your butt up off of the chair, etc, and thrust the gun hand into the pocket. From there, you either draw and fire from sitting, dive back supine, stand up, whatever seems appropriate. In a car, especially if wearing a seat belt, just tuck it under your strong side thigh. If you pick up a hiker, put it under your left thigh, so your right hand can fend him off, block, strike, grab, etc, while your left hand grabs the gun and blows off his head. Best shove the gun right up into his face before firing, cause you REALLY need an instant stop, you do NOT want a hole in your car door (harder to cover up later) and you do not want to risk your hearing to more than one such blast.
The window, you can bust out later, after WD-40ing both sides, and nobody will know when-how it got broke. An EXIT bullet hole in the door, however, DOES mean a shot got fired, to anyone who looks at it. hydrogen peroxide does a pretty good job of getting rid of blood and flesh residues, btw.