谢帝Xie Di - 瓜老外 (Fuck Off Foreigners)

As Kuro said below, gua (melon) is an insult meaning stupid (though in Sichuan it is used to mean a drunk, and this song is specifically about drunk foreigners, or party boys/fuckboys, who come to Chengdu to harass women). Xie Di is from Chengdu, all the best Chinese hiphop is from CDC or Xinjiang (in my opinion).

In Chinese, plural forms are almost non-existent. The name of the song is 瓜老外, in which 瓜 means stupid, 老外 refers to foreigner (or foreignerS, see? that's what makes things tricky). However, in this context, "瓜老外" refers to a specific type of foreigner, rather than referring to all foreigners in general.

Melon means stupid, in Mandarin it would be {傻瓜|shagua} meaning stupid melon. Xiedi is speaking in Sichuan dialect