One place I worked we had two groups having a nerf war. One night at 5:01 I heard a bunch of popping and yelling, I asked somebody what was going on and he said the testing department had just launched a sneak attack on the project management team. The next morning they were still finding nerf darts under desks and behind plants.
The nerf wars ended soon after that because the bosses thought they were wasting company time. They weren't really, all attacks were done after hours when people were staying late. But bosses get to decide such things.