He wants to read me but I can't read him?

My friend is trying to read my body language since then, so we can see through it or ask why I did it now. Yesterday I also tried to observe him for a moment, he was at his laptop and me at mine. He then briefly smiled at one thing and I was just interested in why he smiled. He went out of his skin and said that I do not know and it is too strenuous to think about it. I can't understand why he reacted like that? He always wants to read me by body language?

To read someone means to understand and not to constantly ask why you have now… And why now…
Something annoys

He also has a certain level of privacy. Of course, you may "read" him, but I would not address him for every little thing.

Waddle on!

My friend is trying to read my body language since then, so we can see through it or ask why I did it now.

For me that has nothing to do with "reading" - it is a pure control attempt. To read somebody means to immerse oneself in him and to understand his body language.

This actually happens constantly and unintentionally - without the intention of looking through the other or questioning the reason for his behavior.