Cantonese. Originally as 竹竿 (zuk1 gon1, “bamboo pole”): “bamboo pole” > “Chinese person raised overseas” (the inside is hollow like bamboo poles, signifying the lack of Chinese culture in their knowledge).
The word was changed to 竹升 (“bamboo rise”) for taboo reasons, since 竿 (gon1, “pole”) and 降 (gong3, “to reduce; to lower”) sound alike in Cantonese.