As far as I know there are no rules. Men traditionally wear poppies, any other flowers, medals, badges such as pilots' "wings" etc. on the left because the left lapel is the outer one and the decorations will not be squashed or hidden. The breast pocket of a suit may flaunt a handkerchief, and that too is on the left.
Ladies' clothing is more variable and it's up to the lady where she chooses to wear her poppy.
I'd far rather see a person wear a poppy on the "wrong" side than for them not to show they care at all.



