This image stopped me because it's a cute little kid pointing a gun in my face. The contrast is striking. I also appreciate how well executed this image is technically...it's got great composition, color, and perfect exposure.

Felix Ordonez Ausin/Reuters
A child dressed as Spanish Civil Guards take part in the "Fat Thursday" carnival celebrations in Burgos, northern Spain February 15, 2007 (Felix Ordonez / Reuters)