Tzeentch is the master of all futures and alone holds the key to victory and defeat...the other gods' belief in their superiority is merely part of the great changer's plans
Or Marduk... Or Kor Phaeron... Or Lorgar... Basically, all the Word Bearers will kill you for your impiety. Though the nice ones might just try and convert you using "assisted instruction".
Well, I was thinking something more torturous than door-to-door Chaos Worship, but then again... What is more agonizing than someone coming into your house to try and explain the nature of their belief to you, and also explain just why you should totally hop on the same bandwagon?