When the fish are bigger then the cats.
If the reason you bought the cats was only to help you watch the fish.
If you love the fish more then your stupid gf or car.
If you fantasize about making a giant river that goes right thro the middle of your house that connects your front and backyard pond.
If you feel your fish are your children and if somebody even thinks about hurting them well. lets not get all crazy.
And Finally you talk about the size of your fish like the size of your dick on MFK forums.