In many countries, the “thumbs up” gesture is akin to the middle finger in America. One of those countries is Iraq. So picture this.
American troops, in their tanks and Humvees, are driving through an Iraqi city. From the street and windows and rooftops, Iraqis can be seen giving American troops a thumbs-up. The American troops smile at what they perceive to be a welcoming gesture, and they return the thumbs-up.
When actually, all both sides are doing is flipping each other off.