Rarely, taking down an enemy and his horse at high speed might cause both to rag-doll bounce away ridiculously.
A lord's party might be trying to travel towards a castle or town you're currently putting under siege, but he might be too afraid of you to get close. Watch as he spends the entire siege getting close, then running away, and repeat.
Half frustrating, half hilarious, this almost always happens when you attempt a siege with only one ladder. The entire column of men gets stuck trying to walk up the ladder (sometimes even without any defenders on top). If you were to try to join in on the fun, you'd usually get pushed outwards and fall off the ladder.
In the arenas, two archers often spawn right next to each other. Watch as they put their bows away and ineffectually swipe at each other in a vague approximation of a fist fight, until someone else spawns and clots the both of them over the head with a proper melee weapon.
Can't see over the heads of your men to shoot the enemy? Want to fire an arrow over a hill without exposing yourself for too long? Ready a shot, jump, and release. You're accuracy stays as perfect as if you were standing still, leading to the amusing mental image of the powerful and wealthy warlord hopping in place, intermittently shooting arrows while the rest of the soldiers look on.
If you ever enter a tournament in one of the Swadian cities, there's a chance one of the fights will have everyone on a horse with a jousting lance. The AI horseback pathfinding seems to have problems with walls and generally doesn't understand couching lances, so the matches often end up with everyone but you crowded around a single corner, ineffectually poking each other with their lances until you break them up.