Practice confrontation without loosing your cool, by yourself, before an incident happens.
And don't necessarily wait until something happens to "protect" yourself. If someone's coming over who tends to, say, eat your food, then when they head towards the kitchen tell them calmly but in a tone that brooks no disagreement, "Don't eat my food."
Don't let them make you explain anything, "Don't eat my food" is pretty self-explainitory. You don't have to defend yourself. Just make the statement, calm and confident, like there will be no arguement--sometimes that alone prevents *discussion*, lol. Do not let them drag you into a discussion. This is your rule, the end.
Then think of other rules you need to enforce for your life to be the way you want it to be. And do it.
