My favorite hitbox "issue" is the 1h thrust. Thrust directly at your target, it will either phase right through them or glance. Thrust at open air to the left of your target (their right)=hit.
Don't even get me started on throwing projectiles. I've gotten headshots on an axe that's clearly flying over someone's head, but the axe that actually hits their head, counts as a torso shot. It's not like you can aim throwing axes anyway, but funny nonetheless.