Can't say I have every really thought of it, I do most of my reading (at least pleasure reading at home. Generally I have a goal when I have gone out in public and it is not reading. I might read outside of my home, but it would likely be somewhere secluded and not so public. (Also I drive no reliable and frequent public transit in my area).

Still, I think there are some books and topics I would rather not read in public. Or at least I would rather the public not know that I am read, be it a false cover or on a kindle.

I don't read any erotica or romance novels in public. Not because I'm embarrassed per se, but I don't exactly want to be turned on in public on a regular basis.

I've been reading romance novels since I was 11 and I love to travel. Despite my severe social anxiety I have always read that sort of thing anywhere that I wanted to.

I can't read Anita Blake books in public because I know they are just horrible. But it's like a train wreck I can't look away from.

I would and have read everything except graphic (as in actual pictures) porn.

I was reading a "literary" book once that had a lot of pictures of penises and that was interesting.

Pretty much anything I want so long as the cover and title are reasonably discreet (or I put one of those book socks on it), but I'm not sure I'd read anything that would arouse me because I wouldn't want to be sexually frustrated in public. xD