No hard drugs: A big chunk of my immediate and extended family smokes weed, so its all good if you do too, but anything truly hazardous to your health and horrifically addictive? Yeah, no. That's not gonna fly with me.
No pressure: I don't drink/smoke, and you must respect that. The moment you try to coerce or force me into drinking with you, or really trying ANYTHING I don't want to do, we're done. You can ask, but a no means no.
Racism/Sexism/Homophobia/Transphobia: NEIN! If any kind of hate directed towards these issues comes out of your mouth, be prepared for a wicked verbal assault and a swift kick out of my home. Or me turning and leaving, depending on where we are.
Be Open-minded: I like a lot of strange and wonderful things, ranging between keeping a collection of skulls (real and fake) around my room to watching MLP: FIM religiously. You don't have to enjoy everything that I do, but you need to be open to it.
Cats: You don't have to be a cat person. You might even convince me that we could keep a dog. But it better be a dog that gets along with cats, because I will never be without one. I will take in strays, I will feed neighbourhood wanderers, I have catnip growing in my garden. I have never been without a cat, and I never will be. So any allergies to cats? Sorry, but we're just not gonna work out.
Gaming: I am glued to my gaming systems. There is nothing you can say to convince me to part with any of them. You can join me and we'll have fun tearing up the online world, but if you're not into that kind of thing, then you need to be ok to give me space to play.
Writing: I'm a writer, and sometimes I write smut with other people. This doesn't mean that I feel any less for you, nor do I feel sexual attraction to the writer on the other end. I just enjoy writing, and a lot can be conveyed through sex. It happens. Be ok with it.
Speaking of sex: I'm not real big on the sexytimes in RL. Honestly, sex is a bit terrifying to me, seeing as I have no experience with anything relative to the actual sex. I've had a girlfriend. I kinda know how things work, but we didn't get very far. Kissing, cuddling, clinging; that's all good. Intimate parts meshing? *Flees*