Ambidexterity is one of Fallout GURPS advantages. See: Fallout GURPS.
You can use both hands with equal skill. You do not suffer the -4 DX penalty for using an off hand like most people do, and can fight (or act) with either hand (though not necessarily both at once). Should some accident befall one of your arms or hands, assume it is the left one.”— Steve Jackson Games GURPS sources
With the abandonment of GURPS, Ambidexterity was removed, image recycled for Fast Shot.