Should I wait until they mention something like it or just out of the blue. And should it be privately or not?
Drop hints and when they ask go like this "oh yeah, i am actually" and then talk about something completely unrelated. Like, it's no big deal. If you don't make a big deal out of this, then chances are your friend also won't. Just FYI, do it while out in the city, walking and stuff...
I came out to 2 friends, both males. 1. I had a pic of me and my niece hugging on my laptop screen and he was like "that your gf?". I told him yup..He was like "cool" Later on, i told him tht i really was into girls but the pic was of me and y niece. For the second, he was like "gay is so wrong". I said "huh, you hate gays so much? What if i told you i was gay?". He said "well, for girls...that'd be pretty cool". I'd suggest you waiting until the appropriate time comes up.. then you just tell him/her. I also don't assume you would shout it out across the hall or something. As i said, when the moment presents itself, you just take your shot. Good luck