I tend to point fingers at people like that and laugh so they can hear it hoping they'll pick it up and understand it's bad for them.
Group of friends in pub, couples at restaurants.. everyone with their noses in the screen or taking photos of every stupid little moment (Look FB, I'm having this cake now, like me). It.is.mental...
I started ignoring the people after there complete focus went to the phone. And they learn quick. Suddenly they realize they are behaving very anti social.