OK, that guy must have not been thinking, or not aware of how the system works.
It was a long time ago, and I don't remember the details but I think I questioned his field of expertise. He was talking about having sleeping problems, and he wanted to do something about it, so he asked me some questions. He was thinking about taking sleeping-pills, and I questioned that decision. And he snapped, because he has had sleeping problems for years, and I guess he considered himself an expert in that field - like I was questioning his knowledge. Which would piss me off too, but then again, I wouldn't bring the subject up with somebody if I wasn't prepared to hear that persons thoughts.
Whatever, it ended up with him saying "I love you" to me, so maybe he realised that he'd overreacted. Dunno.