Over driving a car and being overly aggressive are usually displayed by the car pushing or losing front grip at turn-in, missing an apex by 4' or more or having to delay throttle application to continue to steer the car back online after apex in order to keep the car on track. Over aggressive throttle application will be indicated by throttle induced oversteer (slide/drift after apex to exit) or understeer (push from apex to exit). Other indicators of over-driving are white knuckled tight steering wheel grasp, abrupt steering inputs, tunnel vision and driving by the nose of the car.
An over-aggressive driver should be encouraged to relax, breathe, slow down, look ahead, acquire good reference points and slowly add more speed within the limits of holding the ideal driving line.