Tube reading

Is it ok to read pornographic novels on the tube? Well perhaps not quite pornographic but certainly graphic. In my current book-reading surge I picked The Crimson Petal and the White off the to-read stack. Little did I realise that (despite the back cover saying it was about the rise in society of a prostitute called Sugar) it was going to go into steaming detail of sexual encounters every 10 pages or so. I'm trying not to let anyone read over my shoulder in case tehy catch sight of all the spewing, juicy, slicks and nipples peppering the unnaturally white pages from which text leaps blindingly out.