Some people have probably run into this, but this was the first time I had seen it. It's pretty amazing to see something new after playing this game for over 5 years. The following pictures shows you 2 ogres chasing each other around a barracks.
This screenshot was taken by my brother on the map Great White North. After razing the enemies Hall in the top left corner he patrolled his remaining ogre at the barracks seen here. The enemy (aqua-colored ogre) patrolled his as well. The 2 ogres ended up on the EXACT opposite side of the barracks. So what happens? The ogres end up chasing each other around the barracks endlessly. In this example, the ogres made it around the barracks about 5 times before a newly built enemy ogre broke the path.
I haven't tried testing this with anyone, but I'm willing to bet you could set this up again with a few tries. Remember that these ogres were not clicked on each other, and the players were unallied.
-Thanks to Wrexsol (my brother)