It's very important when you're a devilcat to consistently and persistently annoy other cats. This can take the form of hissing and howling through windows (if you're confined inside), or physically terrorising other felines.
The latter is particularly important when those felines invade your territory. DO NOT STAND FOR THIS. The moment you see one coming your way, you must attack attack attack immediately. Hiss, growl, snarl -- whatever it takes.
But it's also fun just to annoy them for the sake of it. You can do this by either taunting them through the window, or invading their space in return. You've got to show them who's boss all the time.