15mA is the limit in my brain. Im sure someone will chime in with a different number but its around here.

The thing to remember is the output impedance. You can have 1000's of volts at a node, but its sourced by a VERY high impedance output. so when you touch it with your hands (which is like 100kohm on a dry day), the voltage collapses because of the voltage divider your hand created.

But if the output impedance is low (transmission lines), well its game over.