Honestly, it’s pretty great when they introduce this brilliant detective character, and he’s a complete weirdo who can’t even sit in a chair properly. In a generous reading, it communicates how he’s putting negligible effort into social norms, implying he’s either completely blind to them… or acutely aware of them, but unswayed. So all the sociopathic charm Light can muster becomes the baseline L expects when trying to model how the killer would act versus how an innocent suspect would act.