They are very funny videos and to a degree correct scientifically but his is strictly "pratt-fall" comedy and vastly over done. We had van de Graff generators that could build up 1,000,000 volts or more with perhaps a miliamp of current for a milisecond. At best a sting. Static sparks in winter can easily exceed 20,000 volts. Tesla coils on the other hand produce similiar sparks at similiar voltages but at much higher amps and for as long as contact is maintained. A very dangerous condition and potentially deadly.
In general voltages above 50 volts are potentially deadly and if wet under 40 volts especially if the current flows actoss the chest. It only takes a few millijoules of energy to disrupt the heart.
Power (in watts) = Joules/Second = (Joules/Coulomb) x (Coulomb/Second) = volts x amps = number of Watts (Coulomb = 1.6 X 10^19 electrons) (1 ampere = 1 Coulomb / sec)