People in here comparing looking at porn images in public as if it's comparable to a smutty book. I dunno, man. It would take effort to read someone else's book in order to know what it's even saying. But pulling up a pornographic image doesn't take any work to comprehend. One requires hovering over someone's shoulder, getting in their space, and actively trying to figure out what they're reading. The other requires no more than a glance around.

As far as being appropriate in public, they really can't be compared.