climb a high building and use space to jump of the building and repeat this step in till your dead on the floor

also can just jump into some flames in till your dead on the floor

If your lucky you can find a toxic pool and if you do jump into it and wait in till your dead on the floor

If your lazy u could just go outside make some noise and just wait in in till your dead on the floor by zombies

You can also run into some people that don't like you if you try to hug them they will:
1.Shoot you in till your dead on the floor
2.Beat you up in till your dead on the floor
3.Throw STUFF at you till your dead on the floor

If your close to water you can always just go to a very deep part of the water and stay there in till your dead in the water.

On the map you can find traps and broken electronic devices, if you get near them and turn them on you will be electrocuted till your dead on the floor.

If you can find a explosive barrel you can attack it which will blow it up, repeat this in till your dead on the floor.