THIS IS DIFFICULT BUT NOT IMPOSSIBLE
Bend your wrist towards you—see where the crease is? Go for there, one diagnal cut, as deep as you can make it; try a razor. Running a hot bath will increase blood flow to the area and bring the blood vessels/arteries closer to the skin, making them easier to cut.
The best way to do it is this:
Get a very large bowl, full of ice water… lots of ice.
Put your arm in it for an hour (hurts at first, then goes numb),
Get a razor or sharp knife (an X-Acto knife is good).
Cut along the wrist where it meets the hand,
Then cut 45 degrees down across your wrist.
Then down center along your arm until it starts to hurt.
but this is not my way