Of course coming out is often difficult for gays and lesbians too, but they do have some "quiet" options not available to bisexuals. A lesbian who chooses to have a "boyish" hair cut and wear butch clothes is likely to be assumed to be a lesbian. A bi woman who does the same will also likely be assumed to be a lesbian, and will remain closeted unless she comes out as bi. A gay man who shows up at social events with his boyfriend and introduces him as such is going to be seen as gay. A bi man who does the same will be seen as gay too, and will still be closeted unless he comes out as bi.
Gays and lesbians can also put rainbow flags or an equality stickers on their cars and be out as homosexual. Though the bi community has relatively recently come up with a flag to represent bisexuality, it's still so new that only other bisexuals who are involved in the bi community (a mostly on-line presence) recognize what it is.
So being out as bi is usually something that has to be more directly addressed. Still that doesn't mean there aren't subtle and less stressful ways to go about it. I'll share some examples from my own life to show what I mean.
I met a woman recently who's new in town. Upon discovering she is doing public relations work, I mentioned my experiences with building up a blog. I went on to mention that my blog has gotten a lot of traffic from reddit; mostly from the subreddit "Bisexual," and that I was blogging about bisexuality because the main character in my novel "Love, Sex, and Understanding the Universe," is bisexual.
The conversation could have gone differently. I could easily have not mentioned the word bisexual. Knowing that bringing up my blog might lead her to ask more about it, I could have never even brought up the blog at all. But in fact, I made a conscious decision to mention the it, and made a conscious decision to use the word bisexual. To have navigated conversation away from where I saw it naturally heading would have been closeting myself. Instead, by allowing the flow in that direction, I instantly outed myself to a new-found acquaintance in a non-dramatic/traumatic way. Sure I didn't make it 100% clear I'm bi, but she'd have to figure I likely was. If she wasn't comfortable with that, I'd know right away, and could dismiss her as a potential friend. By going this route, I also avoided ever having to decide if and and when and how to tell her, somewhere down the road, about my sexual orientation.
This is how I've mostly come out. I know I'm lucky; I come from a relatively progress and non-oppressive background, and I've always lived in progressive and non-oppressive places. As a result, coming out has been mostly a non-event.
Sometimes coming out can just be a matter of not hiding. One night, years ago, I was kissing a woman on the sidewalk a few blocks from where a big event was occurring. Someone we knew was walking by and she tried to conceal my face, thinking I was trying to pass as straight. I told her I didn't have anything to hide. Again, I outed myself just by not making it a point to closet myself.
This simple act of not hiding also occurred a few years ago when I was exchanging comments on Facebook with a friend who knew I was bi. All the sudden, he went to private messaging because he wanted to ask me something that he knew might out me if done publicly. I told him that the fact that my bisexuality wasn't known by our mutual friends wasn't due to any efforts of my own, but rather because people made assumptions, and I continued the conversation publicly. I'm not sure if anyone was paying attention, but if people who knew me to be in an opposite sex relationship saw the conversation where my friend asked which female actresses I thought were hot, they would have had a good hint I wasn't exactly straight.
In fact, many people I know just found out recently that I was bi when I set up a Facebook Author's Page for a bisexual themed novel and posted links to my blog about bisexual issues. Again, a non-dramatic/traumatic self-outing. I just thought well, if they hadn't figured it out yet, they'll know now.