I had three basic rules when my kids were little:
1. By all means feel free to express your emotions, but if you're talking to me or other adults I expect you to speak in a civil, respectful, way.
2. If anyone (particularly adults) treat you in a way that you know isn't right tell me.
3. Don't do anything that will hurt or harm anyone else, animals, and/or someone else's belongings/property (with the absolute most important part of that being not to hurt other living beings with feelings (like people and animals). Kids aren't always capable of anticipating what activities may "harm" someone's belongings (for example, playing ball in the living room can seem like a good idea to a kid, until Grandma's vase gets broken). Kids can very easily and readily understand, however, the kind of actions that will hurt another person or a pet (at least once they're past a year and a half old or so, or are at least capable of understanding language enough to understand the rule.