kick a baby, kill a puppy, rip out the ribs of the damned priests that bless off on the foolish armor! Destroy not only their bodies but kill their family and destroy everything they hold dear to!! Eat their flesh as they still live, carve out their leaders hearts and eyes in front of them, force feed little tiny pebbles to them...o.0 then after that...if they live ask them nicely to join the right side, the chaos side!!
oh and dont forget to carve out some flesh in their leg and place in a pound of crushed glass, stich it back up and make them run off =D sharing is caring. BLOOD FOR THE BLOOD GOD!
Having some true Chaos typed quests and such realy spices up the faction. because most evil is a very boring form of evil in games
Turn out all the lights in the enemy fortress, steal the boots of their power armor and generously cover the floor with lego bricks. With nails sticking out of them.
That or use Holy Promethium to warm all the ale an Astartes chapter owns. I can hear the tears already. Don't try this trick with the Sons of Fenris though. Unless you like a Frost Axe up your backside.
The Sons of Fenris are far to busy being wolfy wolf wolves* as if that they could harm anyone. If you really want to punish them, throw in a single she-wolf in heat and look how they will tear each other apart. *(= yiff yiff yiff )