Use of the word is similar to the words "cool" or "excellent" and it comes from the root word "decent".
An alternate spelling is dece, but the spelling with the extra "e" in deece is typically used to reflect a higher degree of satisfaction. In this form it is pronounced with an extended center long ee sound.
disc golf yesterday and I aced hole 9."
Guy 2: Dude stop saying that! I don't know what it means and it'll never catch on!
Guy 1: That is soooooo not deece