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Jyutping m4 hai6 aa3 maa1
Pinyin wú xì ya ma

Definitions (Wiktionary)
  1. phrase, Cantonese
    No way!; You've got to be kidding me!
    (syn.) 唔係呀話, 唔系呀话, 唔係呀化, 唔系呀化

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Jyutping m4 hai6 aa6 maa5
Pinyin wú xì ya ma

Definitions (CC-CANTO)
  1. surely it can't be; it can't be true, can it?; you must be kidding; you gotta be serious; seriously? you got to be kidding!; really? That can't be! [colloquial]