I am from Sheffield originally and always thought deedar was a derogitary term that people from Barnsley knew us as due to the difference in pronounciation, ie a true Sheffielder prunounces 'th' as 'd' - what dy doin dee, Barnsley - what thy doin thee, normal English - what are you doing. Or dee n dar, thee n thar, you and me. Sheffielders refer to Barnsley people as Dingles, not a clue why :/