Why does my cat hiss at me?

I can count on one hand how many times my cat has hissed at me in 3 1/2 years. It has been when I have picked her up to take her home from somewhere she wants to stay (under a neighbor's bed whose house has been rumored to have mice),once when I wouldn't let her out to play with a Tom Cat etc...What I mean is she has to be denied something she thinks she would die if she couldn't have at the time. Or if she doesn't like someone picking her up who she perceives as her enemy. You have to figure this out. You are doing something extremely against her nature or her well-being. If you have established yourself as her enemy, you better do something to reverse this ASAP. You have to have some idea why this is happening because it is a reaction to an action.

Our calico cat adopted us about 2 years ago. She was an outdoor cat, she moved in, and only goes outside for a couple of hours a day, and almost always stays within our fenced in backyard. She never goes out at night anymore ever since she got bit by something in the head which cost me about $400 and almost killed her. Anyway, my cat and I are now very close, but when I go out to the backyard and start teasing her by putting my hand/fist near her belly while she is laying on her back, she may hiss at me, or fake bite me and try to claw me. She never breaks skin on the bite, but her hissing did get me mad, but it was my fault as I tease her, she seems to be only protecting herself. I walk away when she hisses, and a few minutes later she comes back in like nothing happened.
I don't think the hissing is very serious, although is sounds very nasty!

Might be hurt. Check his/her body for injuries/abnormalities. (Wear gloves in case of scratching)

If she/he hisses when you try to pick her/him up or start patting a certain area, it might be an injury of some sort. Otherwise she/he might just want some leave me alone time, or be mad. Some cats have incredible personalities, others just act really independent.

I have a stray feral cat that adopted my back yard. Every morning she greets me at the door, and lets me pet her knowing I'll give her some food.

After I pet her for a few seconds, I grab the food and walk outside to the bowl. It is when I'm heading to the bowl that she hisses at me. She knows the food is coming, so I don't think in this case she's angry or scared (impatient maybe...lol)

My gut tells me it's just a defense mechanism she adopted when she was feral before she met me... when I scold her for hissing, she just meows...

If a cat hisses at you, it means one of the following:
it has an injury where you touch it
its mad
it gets startled by you.
To know what answer it is, here are syptoms of these reasons:
Injurys: it trys to block you from that spot
Mad:it has folded ears and deep voice
Startled: puffed up tail and backs away and hisses.
I hope these help!