I guess I'm "lucky" because most people that know me knows I have bp. Many of my coworkers know, my supervisors know, many family members know and most of my friends know as well. My illness doesn't define me, but it is something I struggle with. And you have to laugh about it sometimes so it's not so overwhelming. My goodness look how many pills I'm on! That is my joke around the office.
The only time I was hesitant to mention it was at my previous job due to ignorance and lack of education of those coworkers. Only a select few knew.
I have to build up a certain level of trust to tell someone, but then again I try to educate those that don't understand. Bring on the questions! And if you dont believe in mental illness issues, then thats your problem and I leave it alone. Stay in your ignorance. My circle of friends is small and I'm not on social media, so it is not broadcasted to a wide audience.
Everyone has a different set of circumstances and comfort level, so it can vary on who you decided to tell or not. But the choice is yours and yours alone.
Oh and when people use MI as an adjective and they're in my pressence, I will call them out and school them on how they should not say stuff like that! I hate that! I've called my mom out a few times when she's done it. Sister too.

Edit: And I'm not bipolar, I live with bipolar disorder.