grammar - Why you're laughing vs Why are you laughing?

Recently I was talking to my friend in English. He started laughing and I asked him Why you're laughing man?

Someone told me you should say Why are you laughing? and this one is totally wrong.

I got a little bit confused. I know "Why are you laughing?" is correct but I can't wrap my head around it fully that mine is totally wrong.

I represented what I meant through intonation of the sentence and my buddy had no problem understanding it. my question is:

The form I used was totally wrong? and I should stop using it?

I'm guessing in written English this form is wrong and if I use it, it's gonna represent a statement, but in the spoken language, since we have intonation I thought it might be unnecessary to emphasize on being totally grammatically correct for every sentence I'm saying.

Am I wrong?