pmj1989, yes, it is!
Should I say, just perfect or just nearly perfect?
I never thought that the given problem to "de-dup" an item list could be solved with such a small linear expression. Regular expressions can be really mighty.
I modified the expression a little bit to work with multi-line textfields too, but I have not tested it in full depth.
(?:(?<=,|\A|^))\s?([^,]*),(?=.*?(?<=,)\s?\1(?=,|\Z|$))(?#de-dup comma- or comma+space- delimited list)
DD.20100924.1456.CEST