One might think (judging by this photo), that the cyclist is unaware that he is being spied upon, however I must assure you that this is not the case.

The object that I am photographing through is very small, and could not conceal me from even the most distracted passer-by. The cyclist is looking at me in puzzlement, because he sees a grown man attempting to hide behind a small fence-post in broad day light. Only once he has past me and risked a backwards glance does he realise that he is has been involved in an experimental photograph.
How could I take this concept further? Perhaps I could go on the London Underground dressed in an absurd costume (e.g. Giant Lobster, Ballerina, Aphid, Monkey ), and secretly take photos of people as they gawp at my akwardness.