*The exploit requires you to be HAT speced and it also requires an AoE pack, or at least another target apart from your main target!*
Okay, first of all I'm not 100% this is an exploit but as far as I know this isn't supposed to happen. What I noticed when I was AoEing some mobs while waiting for my raid to get together was that whenever I critted with Fan of Knives on the mobs I hit with Fan of Knives (except for the current target) I gained a combo point. I found it especially handy while AoE farming since I could kill the mobs I was attacking faster than usual, but it could also be used in raids / instances to get some extra fast CP regeneration.
EDIT: After a while of testing on training dummies I've noticed that the combo point gain for some reason only happens when the Main Hand weapon crits. Added another SS to show it.
P.S. Please correct me if this isn't an exploit