Capacitor when short circuited
You can think of shorting a charged capacitor like you would shorting a battery. When you short a storage device the only resistance in the circuit is the tiny resistance of the wire and the ESR (Equivalent Series Resistance) of the device itself. Assuming a perfect short, the current would be limited only by the ESR which tends to be very low. The high current through a low resistance causes significant heating due to the power dissipated by the ESR, determined by P = I^2*R. This heating degrades the capacitor and can cause long-term damage. You should always discharge a capacitor through an external resistance to limit the current and minimize heating.