I am not commenting for you
I am not commenting about you
Someone was talking crap on my Facebook comments when I asked him why he was doing that. He said “I am not commenting for you”
Shouldn't he have said about you?
They mean different things, assuming the writer knew what they were saying.
I am not commenting for you
-> My comments are not for your benefit. You aren't the intended audience. The comments are directed at other people, for their entertainment.
I am not commenting about you
-> Like you mentioned, if the comments were about you or not.