The definition of duplicity has actually been sort of forgotten by a lot of people. It is very close to the word duplicate and this makes it harder for people to get the true meaning behind it. Duplicity means the idea of double dealing or hypocrisy, not performing by your own standards in the same situations that you expect others to act like you during. This complex meaning also has its place when it comes to dream interpretation.
If you have a dream about duplicity then this means that you need to be more upfront about your feelings on a subject because your duplicity that you have been using in real life has gotten you nowhere. This is the act of being very concealing about your actions and unwilling to share your true thoughts with others, instead resorting to being intentionally secretive and annoyingly hidden with your motives in order to further your cause, whatever that cause may be.
To dream that you are a duplicitous person then this can mean that you feel like you have not been a good person lately or you have taken advantage of people for your own self gain. The worst part is, you see yourself as two different sides, your good side and your bad side. You can morph from being caring and compassionate to being cold and calculating at the drop of a hat. This might serve you well in the end, but at what cost? No good can come of it and you should do all you can to be more compassionate in the future for your own good.