It's very important to know how to pick the right battles. While many would think Light is someone who needs to know everything, he's much too skilled to ask the wrong questions at the wrong time. A negative sexual experience would just be someone bad at the act, which could bring either awkwardness or even discomfort. It could mean someone became too attached and refused to simply let go. As someone interested in crime, there's a darker avenue it may take. Either way, Light knows this isn't a question to pursue, not in terms of specifics. Maybe someday, maybe never. L had a bad encounter, and it's stunted any current interest. That doesn't erase curiosity. Who was it? Light knows it wasn't Myr; their relationship isn't very good. Perhaps it was a one night stand, perhaps it's someone who isn't in his life anymore.

Perhaps it's Niles, despite the feeling Light has.

"I see the logic of adding it to bonds. Sex can be casual for some people, but it's intimate for most. So are the bonds. One involves sharing your body, and the other involves sharing your mind in a way that goes beyond talking. If affection isn't involved in the beginning, there's a high chance it becomes involved. If you're physically attracted and available, there's nothing left."

By the sound of things, L isn't currently available.

"I'm not going to ask details about your experience, but I do need to know one thing: the person, are they dangerous?"