I though slat armour worked because RPGs only had a detonator in the nose, so unless you were very unlucky and the tip of the RPG hit a slat, the RPG would just jam itself between two of the slats.
I saw that a few times actually, but only when the idiot firing the thing didn't pull the safety pin out of the warhead. The RPG is surprisingly safe when you neglect to remove the safety and will happily fire, but not explode in that circumstance. It was around the height of the Fallujah offensive we saw that happen.