I'm a major nervous type about using a cellphone anywhere in public. One of my biggest irrational kind of fears is being well, "that guy". Or rather, "that girl". I'd hate for people to be irked by me and my ill-modulated voice yelling about some inane topic with some other person while we're all just in line at the grocery. Because really, if it's important, they'll leave a message. One of the primary things I learned in my days, you don't have to answer the phone. Telemarketers, friends you want to avoid, whatever it may be, you aren't obligated to them, just ignore the ring.
If my phone rings while I'm out, I'll pick it up, but I pretty much whisper and explain right away that I'm not at home and can't chitchat. Admittedly, that's my problem, and it doesn't bother me if other people talk on phones in public, I just have too noticeable of a voice to feel comfortable, haha. Anybody else unable to operate a phone properly while other people are around?
As for public bathroom phoning, I wouldn't dare. If I were actually using the facilities, no way, and if I were just milling around outside of them, well, maybe. Depends on if it was empty or not. I always get so unhappy if someone comes into a restroom on the phone. I don't blame them of course, they want their privacy, but I can't even pee without getting embarrassed that TWO people are now privy to my most private of moments.
I know, I'm a freak!