I hadn't heard of this before reading this thread. Having read what it means, I think it's quite sad that somebody felt it was necessary to define themselves in this way. Personally I think it's weird that anyone wants to define themselves in rigid little boxes. I know that I am straight, I have a wife who I love. If I was single I'd still say I was straight, but if I met someone who was transgender and I liked them, why would I kill that stone dead by defining myself as 'superstraight'. Why not be open to meeting someone and taking them at face value as someone you want to spend time with? It's no wonder there are a lot of unhappy people in this world.
By saying you're straight, you're saying you're generally attracted to the opposite sex, which is fine. By saying you're 'superstraight', to me that says "I'm attracted to the opposite sex, and also I find transgender people repulsive enough to rule them out with a blanket statement". Why not just remain 'straight' and keep the rest to yourself? As I say, I think it's sad and there's no need for it.