How can you tell if you have bipolar disorder or just a weird personality?

Level of function. Bipolar disorder is a serious disorder that affects you level of function and has dramatic cycles of energy shifts that last days to months. A personality disorder just affects how one relates to other people. However, untreated mood disorder can look like a personality disorder. Mood charting helps identify patterns along with a psychiatric evaluation esp if neg impact on life.
See my health guide. I have put together a collection of my previous answers about bipolar disorder. Look through those answers then talk to your doctor.