这句英语语法有错误吗？

应该错了

stupid可作形容词或名词（可数）

正确的表达方式如下：
You are a big stupid.
You are so stupid.
You are such a stupid man

SO 后面接 形容词 或者副词 如 so hot .so fast

such 后面接 形容词+名词

可以改正为

you are so big.
you are so stupid.

you are such a big stupid man.
you are such a big man.
you are such a stupid man.

stupid 为形容词。前面不能用啊a,
你貌似把stupid 当作名词 笨蛋了。我查字典了
它只有一个词性 是形容词。
big 不能修饰stupid 副词才能修饰形容词。

可改为：
you are so stupid
you are such a stupid man
you are so stupid a man

1.您的这句话是错的.

2.a是冠词，修饰一个事物，但你的句子并没有在后面修饰什么，应删去a。

3.所以经过1后就成为You are so big stupid.但由于你的意思是说别人反应迟钝,因此不应该用表示大小关系的big ,可以将它删去,变为You are so stupid或是You are very stupid

4.希望我的回答对您有帮助!

you are so big a stupid