If I put the positive probe of my multimeter on earth, and touch the negative probe with my hand, while another hand is touching the metal surface of my MacBook, I get around 22VDC or 69VAC. I cannot figure out why this happens. If I replace the MacBook with a li-ion battery, I get floating readings, if I try with a DC power supply, either positive or negative, I get nothing else.
This even happens when the MacBook is not plugged into it's charger, so it's not being connected to earth at any point. This behaviour defies my understanding of electrical engineering, and I would appreciate if someone could shine a light so I can understand how this is possible.