"When you ask me what I am doing today, and I say "nothing"
It does not mean I am free. It means I am doing nothing."
I had a friend who would ask me this a lot. It was really frustrating because I wanted to do nothing but he took it as meaning that I was free to go and have a beer with him and when I declined he would make me feel guilty about it.
If you ask someone what they are doing and they say nothing. Respect that. They are wanting to be with themselves. It has nothing to do with you they just want to hang out with themselves.
Let them be.