My friend keeps saying she is bipolar, but she clearly isn't. are most people just faking it?

Misconceptions: Bipolar is a serious mental illness that affects about 2.4% of people in the world. There are a lot of people that think "moodiness" is bipolar disorder. Most people aren't faking it, they just have a misconception about what bipolar is. There is no way your friend can tell if she is bipolar on her own. If your friend says she is bipolar, take her seriously and tell her to see a doctor. Best.

The term "bipolar": is sometimes used as slang for moodiness. This is similar to the phrase "going postal" to describe violence. You friend may be using the term bipolar in this manner or maybe she believes she has a mood disorder. Maybe she has been diagnosed as Bipolar? She isn't necessarily "faking". If she is worried about her mental health - psychiatric assessment would help.