you could attach a resistor to the ground wire, and touch the other electrode of the resistor, with 2 resistors appropriately chosen (so that you don't fry the MM), you can put a multimeter across one of them and observe the discharge, or alternatively build a simple circuit that lights a LED as long as the voltage across the resistor is higher than some value... Discharging doesn't need to hurt..

That said, depending on the setup (type of ground system and electronics) it is not necessarily safe to touch the ground from an outlet!