The teacher said that there are thousands of volts of friction electricity when undressing in winter, but why are people okay?

Joke, "No matter how high the electrostatic voltage is, it won't hurt people." You can pick up a lightning bolt and show it to me.

All electricity is the same, and its essence is the directional motion of charge (including alternating current).

It should be noted that there are several thousand volts of friction charge when undressing in winter, but the internal resistance of this "power supply" of several thousand volts is very large, which is much greater than the human body resistance, so the human body resistance is equivalent to being connected in series with that super-large internal resistance, and the voltage in series is pitiful, so there is no danger. Moreover, the charge is relatively small, and the light is guided at once, which will not last long.

Safe voltage 36V refers to the limit of human safety when the internal resistance of power supply is small and the charge is sufficient.

This 36V is also a general idea, which varies from person to person.