What are your hard limits?
A lot of these are standard fare common sense but I have to say my current list is tiny compared to what it was when I entered the lifestyle.
No animals, no children, nothing illegal.
No permanent physical damage.
Nothing life ruining that would prevent things in the future like getting a job, finding a place to live, etc.
Nothing that will prevent me from practicing proper hygiene (e.g. brushing teeth, bathing, wiping after #2).
No sexual contact with other men or their bodily fluids.
As things are, nothing that would prevent me from fulfilling my daily life obligations as a human. (e.g. going to work, paying bills, etc.).
I may have missed a couple of things. I will add to them if I think of anything. I used to keep a running list somewhere but generally speaking I only get involved with people that share the common sense limits. I have some "medium" limits and those would be considered "hard limit unless discussed first." I used to consider soft limits like that as well, but over the years I have discovered that having soft limits pressed or flat out broken can sometimes do some wonderful things for my subspace.