DARKEST OF DAYS 

With Chest Hair Glitch.

With Chest Hair - 200 points 

Complete all the levels in the game on the highest difficulty

I found a glitch that works very easy. Play the game on normal or easy and once you finish and get the achievement for beating the game just load your last save (should be the last level).

1). Go to the settings and switch the difficulty to With Chest Hair.
2). Just beat that last level on that setting and the achievement will pop.
3). No need to play the entire game on the highest difficulty.