Hi Beth,firstly,"哇塞"is not only used in Taiwan,but also used in main three citys-Xiamen,Quanzhou,and Zhangzhou,we call these three citys Minnan Zone,where in the southeast of China-Fujian province."哇塞"is a saying just like "F*ck" in English ,so it's a derogatory term;secondly, I think in your dary "Wow, so rude"here is right,it's acceptable,but wrong used "哇塞".