Student or Learner
Hello, do I need use "an" article in this case? -> "You are an arrogant"
I am not a teacher.
No, but you do need a full stop at the end.
You are an arrogant man.
You are arrogant.
I do see a lot of English learners trying to make nouns out of some adjectives. Many times I've seen something like "He is such a stupid!" I suspect that's mother tongue interference.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.