Unless they're people you're really close with or people who are exceptionally educated on the issue (like a bunch of psych majors), I'd avoid using the word "bipolar" when you talk to them. There are still a lot of very negative associations with that word among the general public and people tend to assume you'll engage in a lot of crazy behaviors which you probably won't. I'd tell them something vague, like that you have mood issues or depression issues, and then ask for what you need from them (time to yourself or whatever). If some of them are really supportive or ask more questions, then you could tell them more details, but by being vague you get to ask them for what you need without volunteering too much information or making them too uncomfortable.