-A Dedar, Is someone who says 'Dis' and 'Dat' instead of this and that. Most commonly used to describe Chavs or people that aren't speaking proper English because their trying to talk in a Jamaican accent Even though they do not originate from Jamaica and cannot speak Patois.
-Another way of describing a 'Jafake-an' accent

It is typically an offensive word, (But it is very light hearted).
Guy 1: Bruv, pass me dat ting so I can do dis innit
Guy 2: Hahaha you sounded like such a Dedar when you said that!

Example 2
*Guy comments on girls fb photo*
Guy: "Yo bbz, I love dis pic"
*Girl see's the comment and says to friend*
Girl: "eurgh he's such a dedar"

Example 3
Guy: This total dedar came up to me earlier, He thought he was a proper G or something!
by TheeDeadMowse December 3, 2013
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