Get 20 kills/assists on concussed enemies aaargh

The stun grenade is useless. Even if you successfully "stun" an enemy, it doesn't have any kind of useful effect like maybe -stun- the enemy and any useless effect it does have doesn't last long enough to get the kill, and you've just announced your arrival with a huge glowing firecracker that sprays confetti. And then if you're fortunate enough to get a headbanger or stun assist, it doesn't count on the actual challenge because the challenges are riddled with bugs.