I got this achievement during the level where you meet the kidnapper on the way to Lover's Peak. As he takes your gun and leaves you with only flares it is definitely easier to get the reaction time right.
You need to wait until your health is almost completely depleted, with the heart beat and gray screen. Then ignite a flare just as a taken is in the process of attacking you (i.e. right as he is swinging, just before he hits you.)