Hmm... I wouldn't go licking the connector. I think there may be some safety relays in the Model S UMC, but I'm not certain. Fairly sure the Roadster 120V Spare Mobile Connector (MC120) had no such relays, nor did the Roadster Foundry type 240V connectors. So there is a possibility that the business end of the connector is live when the other end is plugged into the wall socket.
There is a pilot signal which prevents the car from pulling to much current during charging, as well as GFCI which cuts power if there appears to be some ground leakage current (like through someone's body). But I wouldn't take "no power till connected" as a given, like you can with the HPC. The HPC definitely includes a power relay since you can hear it click (separate from the relay (contactor) in the car).
The connectors are designed to be basically finger safe however.
I agreee, the best protection against electrical shock is to treat ANY power source you are handling as energized. However, there are safeguards mandated by standards that must be part of any device classified as an EVSE, portable or otherwise.
From the Leviton website:
EVSE Fact Sheet: 240 Volt Home Charging Station | Leviton Information Exchange
EVSE Fact Sheet: 240 Volt Home Charging Station
Cord-and-Plug connected EVSE allowed?
Yes, because Leviton’s EVSE charging stations have been designed to comply with all applicable safety and industry standards and also for code-compliant installations. Leviton’s 208/240 Volt AC-rated cord-connected EVSE are part of a system, identified and listed for the purpose, by Underwriters Laboratories. They are also compliant with the requirements of the National Electric Code: Articles 625.13, 625.18, 625.19, and 625.29.
NEC Art. 625.13 states: Electric vehicle supply equipment rated at 125 Volts, single phase, 15- or 20- amperes or part of a system identified and listed as suitable for the purpose and meeting the requirements of 625.18, 625.19, and 625.29 shall be permitted to be cord-and–plug-connected
625.18 requires an interlock that de-energizes the electric vehicle connector and cable whenever the electrical connector is uncoupled from the electric vehicle
625.19 requires an automatic means to de-energize the cable conductors and electric vehicle connector upon exposure to strain that could result in either cable rupture or separation of the cable from the electric connector and exposure of live parts
625.29 requires that the unit be located in indoor sites, including integral, attached and detached residential garages; enclosed and underground parking structures; repair and non-repair commercial garages; and agricultural buildings
Per the requirements, the connector is de-energized when not connected to the vehicle, thou I won't tempt Murry's Law and assume "no power till connected" as a given either.