[you such a..]即係咩..？指教＊

you such a stupid boy.

即係"你真係一個xxxxxxx" (既人) 多數用來形容 "佢係一個點樣既人"

你正一......

意思係 「你呢個… 丫！」

例： You such a bitch! = 你呢個賤人丫!

such 即係(與that連用)如此的.
example::He is [such] a good teacher [that] all his pupils like him.
or
(表示驚歎或加強語氣)這樣的,這等的
It was [such] an exciting game.

hope i can help u =]