Calling people bonderøv for sounding like they're from Jutland clearly makes you one. One of the worst things in Copenhagen is meeting someone born and raised Vesterbro who's never been to Jutland and think that makes them cosmopolitan. (And any likely to be a bonderøv than a conservative 7th generation Northern Jutland farmer).
Træls is a kind of dialect word used more in the rural part of the country (Jylland/Jutland peninsula) and not so much on the island of Sælland/Zealand where the capital (København/Copenhagen) is. It's debatable if it is standard Danish. You risk sounding like a redneck or worse if you say this in the wrong place ;)