"I'm sorry you're hurting, is there anything I can do to help?" works just fine. I prefer people not to mention the SI (if it's done on an obvious place) because then I feel the need to defend it. The worst is people who say, "You know, by hurting yourself, you're hurting me." No. I'm not. I'm hurting myself. I'm not giving anybody else a second's thought when I do it, and it's not meant to distress other people, it's meant to help me at that moment. The last thing I need is a guilt trip.