1) No insulting, harassing, griefing, flaming or generally abusive behaviour.
This includes using weapons, killing players, using abusive language, etc.
Breaking rule 1 will be met with an immediate temporary ban.
2) Don't troll, interrupt or inconvenience people
For example, don't have a full-blown conversation in chat during a race or testing, don't start testing on the same track someone's already on without permission, etc.