I probably had to explain why this statist asked this questions, the chain of arguments.
1) First, I mentioned NAP.
2) He asked: what is NAP?
3) My answer was somewhat: It shall be legal for anyone to do anything he wants, provided only that he not initiate (or threaten) violence against the person or legitimately owned property of another
4) He asked: okay, but what do you mean when you talk about violence? what is your definition?
5) I tried to give the definition of violence (or coercion, or violent force) as an act of a human against a will or without permission of another human with respect to his person or property (to take, use, meddle with or otherwise do something with the body or property...).
6) And then he brought this argument about touching his lungs (body) by my breathing with no permission from him.
7) I tried to fend off it by telling that there was no harm to his body from me breathing.
8) He responded that I still was meddling with his body without his permission so this is violence by my definition, otherwise I need to incorporate "harm" to my definition of "violence". And if I have no logically consistent and universal definition of violence, the NAP is nonconsistent as well...
This is where I stumbled...