One of them is a highly functioning aspie type (only one born from those parents to not be full blown autistic). He just doesn't understand what the fuss is all about. He sees other people together and questions why people go through the effort instead of just wank alone, claiming it looks like a lot of effort. He handles it more like curiosity, asking a lot of questions. He even once had a poor naive (yet highly attractive) woman staying in his home so she'd not have to be on the streets. Even walking around completely naked, right next to his bed, he was completely unphased, worrying more about how people outside who can see through his windows might respond.
Another one strangely enough has a highly reduced sense of smell from a nasal stimulant he was given when he was younger to combat allergies. As a result, the guy's nose is all sorts of fucked up for picking up and telling scents apart (milk going bad is his personal hell). I don't know if it's connected (pheremones, all that), or if he just happens to be asexual with some issues with scent, but he misses a lot of cues that denote flirting, and doesn't seem to really fall into attraction patterns. When he dated someone, they ended up never doing anything physical during the months they were together. Closest he can really go for being into someone is an intellectual attraction at best.