Travelling weekly (weakly even) up and down you get to see some sights, some of which, although unremarkable, you wish had remained unseen instead of being burned onto your retina. Those, for example, where people pretend to themselves that they are virtually alone instead of in a packed train, they glance around to make sure those sitting nearest aren't looking and they completely disregard anyone further away - like on the next set of seats. People more than a metre away don't exist or matter. Up goes the finger. Down it comes, a glance, a roll, a flick and the results have been jettisoned somewhere within the carriage. It must be something to do with body language and the boundaries we imagine around ourselves where we are impervious to others. In terms of the observer - photographers are eternal observers - we can't look away, our gaze whether we like it or not is fixed onto something we'd prefer not to see.
What has this to do with photography? Not much really other than the power of photography can be huge: effecting change in ideas, opinion and behaviour partly because to be caught in the stare of the lens can be so revealing.
Admittedly this train habit, in the history of the world, is not a weighty subject and has miniscule importance (unless you are sitting close by) however I do wonder what the reaction would be should I begin a new series of images around the subject of this flicking business. It might be a form of street photography to stop people in their tracks on the train. I could poll the rest of the carriage occupants - look at this, to flick or not? Probably the reaction would be a broken nose. Mine. Being a coward my response is just to change my clothes as soon as arriving home.
I wonder if Walker Evans had similar problems when 'shooting from the hip' on the subway? Finding among his negatives a percentage of people imagining themselves alone.
Aside from all that I notice the government recently had their own 'Turn Off' campaign.