Just took a walk and was thinking about this, here's my thought process so far:
Libertarians follow the non-agression principle, which states that no one has the right to initiate force against another person, nor to threaten to initiate force, nor to delegate the initiation of force to another party.
If you stop here you have something like what I think is called anarcho-syndicalism, where if I am using a laptop and you take it away from me, that's wrong (because taking something without my agreement requires a threat of violence against me), but if I quite using the laptop, and you take it, you aren't aggressing against any human being, and therefor you're OK.
If you add property rights to this, it simply results in a redefinition of the NAP, where now if you take something that is my property you are making an initiation of force against me, and if I attack you in response, I am not considered the initiator.
So ownership essentially means that no one can do anything to what I own without my permission, and if they do I am justified in responding with force.
Ownership of myself, then, is the equivalent of the NAP, self ownership means nobody can do anything to my body without my permission, and I can respond with force if they do.
If you reject property in material goods then, it means aggression is meaningless regarding anything that is not currently in use by someone (this always includes the body, because there is never a time when I am not using my body). If someone takes a bench lying on the sidewalk, no case can be made against that because everyone has the right to do whatever they wish to a bench that's not in use.
Likewise, if you reject self-ownership, it means all forms of aggression against human beings are valid. If person a tries to assert property rights against person b, person a is just using force against person b for using a toothbrush person a believes is their property, and this aggression is valid.
If person b attacks person a then, for trying to assert property rights, that is just another form of aggression and no more invalid than person a's aggression. person b doesn't even need to believe he is defending the non-existance of property rights, he could just say he felt like aggressing against someone.
I guess the question then is "is person b exercising ownership by responding in this way?". Unfortunately I'm running out of WiFI time now, so I guess I'll have to return to this later :). Again, please correct me if I'm skipping over or misunderstanding anything.
Teach me now how to free
Devils of my sanity
How to drink from empty glass
How to read from empty eyes
Teach me now, teach me well
How to not to cry and say farewell
How to stand straight on my way
How to face the end of a day