My first idea involves a mirror that, each time a subject views themselves, causes a minor defect to occur, e.g. their eyes move slightly too far apart/close together to be considered attractive, their nose becomes slightly too large etc., compounded by multiple viewings. Too many viewings results in being horribly disfigured/mutated, and eventual organ failure. My main worry is it's another mirror, or this same idea has been done.
Second idea, a gong that when sounded causes the subject to lose all hearing ability or the ability to produce any sound (stomping/clapping or even playing an instrument), except for the gong itself. Maybe hearing it again compels them to kneel before it and pray, throw in a religious aspect.