It derived from Hakka linsi - 淋勢，meaning pretending very powderful. This matched with meaning of arrogant and haughty.

Now become make sense coz in Cantonese langsi doesn't make sense, Cantonese langsi - 撚屎， literality meaning poop noodles, a gross activity which is nothing to be swaggered about.

The supposed correct derivation should be langsai instead langsi. Dunno what happened lost in translation.