According to Inès de la Fressange in The Telegraph today, the worst crime against fashion is the plastic bra strap.
"'People walk around pretending they aren't wearing a bra and you can see their ugly transparent straps. They think no one will notice but it's ridiculous', she enthuses."
Not sure I agree with that, but anyway, what is your worst crime against fashion?
I've been trying to think what mine is, and I think it's the 'mutton dressed as lamb' look, in men and women. Loads of it down here in the south especially in the beach bars at night.