不知道马王爷三只眼

Traditional (Taiwan): 不知道馬王爺三隻眼

bùzhīdàomǎwángyésānzhīyǎn ㄅㄨˋ ㄓ ㄉㄠˋ ㄇㄚˇ ㄨㄤˊ ㄧㄝˊ ㄙㄢ ㄓ ㄧㄢˇ

    • to not know how formidable someone is and so offend them

Character by character

Saying俗语俗語

Idiom惯用语 · Widely known

Literally
not knowing Lord Ma has three eyes
Meaning
Not knowing how formidable someone is, and so offending them. Usually a warning or threat: "you'll see who you're dealing with".

Sources