Kiwi_1282001,
Can you be more specific?..... Other than a static electricity charge shock an electrical shock from our home's electrical power source requires a point of entry and a point/s of exit.
Example, in one hand out the other. Or from a hand and out bare feet to a bare concrete floor. Just two examples....
Is your friend touching another piece of equipment or some object that is grounded with his other hand?
There has to be a difference of potential, voltage, between the two contacted objects.
Where is the current flow path?
As for the piece of equipment. Two wire or three wire cord and plug? If three wire is he using a ground cheater?
If a three wire cord and plug is the safety equipment ground on the receptacle connected all the way back to the neutral bus at the electrical panel?
Does he have a multimeter to do some tests?
Food for thought.... Birds perch on high voltage power lines and never receive an electrical shock.
When a squirrel jumps onto a high voltage power line, he runs down the wire without any problem at all. It's the dismount that gets him. In the end while still on the power line the first part of his body to touch a grounded object.... goodbye squirrel.