When someone peppers their Facebook updates around the time they go to, and come back from work - they are 'Smartphone Cruising'.
They're looking for an excuse to pull out their new iPhone/Nexus to show off to everyone in the carriage that they have a Bleeding Edge phone/cell.
They have no friends, but hundreds of Facebook Friends - so updating your status gives a 'Smartphone Cruiser' something to do with their gadget.
Usually practised by male Uber geeks, of The Great Unwashed variety. In the mistaken and laughable belief that women will become aroused.
George: Hey! Melvin is spamming my Facebook feed with his updates again.
Mike: On his way to work?
George: I guess...
Mike: He's showboating his iPhone - y'know, 'Smartphone Cruising'?
George: Uh. True!