洋鬼子 (yángguǐzi): foreign devil (derogatory term…

洋鬼子 originated in the late Qing as a slur for Westerners, peaking around the Opium Wars and the Boxer Rebellion (1899-1901), when missionaries and merchants from across the 'great ocean' (洋) were vilified as 'devils'. 鬼子 alone became a slur for Japanese (日本鬼子) during the Second Sino-Japanese War.

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Today the word is mostly historical or jokey in tone — Chinese speakers may use it self-deprecatingly about Westerner friends, or in period dramas. Used straight at a foreigner today, it is openly racist; used about oneself as a foreigner in China, it can land as cheeky self-mockery.