I'm not really sure this issue I'll explain here is static electricity related: When we touch macbooks we sometimes feel an acute electric discharge. I measured the conductivity of the macbook outer cases with an ohmmeter and found them non-conductive (2009 to 2015 macbook models). My only explanation is that the macbooks have some outer layer of non-conductive material on the cases, and perhaps when these electric shocks happen you maybe brushing (typically with our forearms) on some of the corners where there may be a non insulated and therefore conductive spot on the macbook case. Looks like the person touching the macbook has a big static electricity buildup on their body (we have fitted carpets, which I understand create a lot of static), and then touching the macbook discharges the static to ground through the power adapter, which is also grounded. I would really like to know why this is happening.