I love being bitten too, and I like the marks also. I think probably, at a minimum, you don't want to break the skin at all because of the amount of germs in the human mouth, and then the teeth can kind of grind that stuff into a wound - not pretty. I don't know about soft tissue injury. My own preference for hard biting is on pretty well-muscled places, like thighs, and not so much on really soft tissue like breasts, but I don't know what the injury would be.