etymologically, it comes from the word for "stranger" and is the same name as the german "Wallach" and irish "Walsh" and welsh "Welsh/Welch". Vlachs are also an ethnic group that speak an ancient dialect, and that's one reason why the stupid is connotated (don't speak like a vlach) but in greek the word for stupid is vlakkos/vlakka, which spelled in greek is different than vlahos/vlachos (spelled with chi not kappa). probably more than you wanted to know--and my family changed it FROM flessas TO vlachos