Save this for the second playthrough on Survival or when you already had the good ending.
To get this ending, you have to fuck up every "good" decision you made on the first playthrough. I have done at least the following things to get the bad ending.
(Sometimes you get a good point no matter what. :)
(You will get a good point for instance at the Undercity level when you enter the first elevator, no matter what) You can get negative moral points for shooting at the Nosalises (those big dog like creatures) in the Undercity level, even the ones when riding down the first elevator.
A negative moral point can be recognized by a little fading to black screen, or the Little One making a comment how sad he finds a bad decision, but accept it is human to make such decisions.
It can get a little confusing at times, since the loading screen shows another title than the level. Check your diaries. It should light up right where you are at the moment.
Reich:Kill the nazi at the end of the level who surrenders right after you got through the door after the chase and you step inside the train cart.
*Separation: Kill the man reading a book in bed who surrenders after you passed a bunch of guards.
Facility: Kill the nazi in the meat locker who surrenders.
Torchlight: Leave your lamp out during the lift ride.
When you get out of the elevator, leave your flashlight out. Don't help Pavel when he's pinned down by the spider.
Contagion:
Depot:
Dead City: Kill both the Demon and its baby, will give you two negative moral points.
Red Square: Shoot and hit a Watchmen climbing and hanging on the Cathedral.
Leave Pavel for the souls instead of grabbing him (It's the part where Pavel begs for his life)
The Garden: Leave the mother mutant bear to the Watchmen and don't intervene when she is overpowered by the Watchmen.
There are some more bad choices but these are the ones that give you the bad ending achievement 100%. When Artyom can throw over the switch at the end of the game you have done it right!