The safest way but a bit slow is to drill a row of holes close together horizontally across the middle of the tile then use a small screwdriver to join them up you can then do any prising from the middle with less chance of damage to the adjoining tiles.
Quickest way is to remove the socket (power off first of course
) and slip a screwdriver blade under the edge, waggle it (technical term) to and fro a bit and the tile should lift and crack across the centre. Eye protection is advised, if you hold a rag over the tile as you do it you should catch most of the sharp bits you will only find later in bare feet!
I notice it looks a bit like you have tiled flush to the shaver socket. Should you ever need to change it that will be a problem.
I usually bring the sockets forward a bit, you can get longer screws if needed and tuck the tile edges under the socket. Just be careful not to get adhesive in the fitting and of course be careful about damage, loosening of connections or strain to wires.
aferwards when grouting the grout will form a seal around the fitting to prevent moisture creeping down the back, but the thin strip of grout will not prevent the unit being changed if needed.
Of course if you prefer not to touch the fitting that's fine but you will need to spend some time cleaning out the grout before the sparks arrives with his big screwdriver to lever it out
