YOU SAID:

i bet your really stupid and cant read my grammar

INTO JAPANESE

私はあなたが本当に愚かで私の文法を読むことができないに違いない

BACK INTO ENGLISH

I bet you're really stupid and can't read my grammar

INTO JAPANESE

あなたは本当にバカで、私の文法を読めないに違いない

BACK INTO ENGLISH

You must be so stupid that you can't read my grammar

INTO JAPANESE

あなたは私の文法が読めないほどバカに違いない

BACK INTO ENGLISH

You must be so stupid that you can't read my grammar