Apparently, thinking about sex can make some people sneeze uncontrollably. I have an admission to make, I suffer from uncontrollable sneezing too, however it's not because of thinking about sex.
I suffer from Autosomal dominant Compelling Helio-Ophthalmic Outburst (ACHOO) syndrome, also known as a photic sneeze reflex. Basically sudden exposure to bright light makes me sneeze. The sun is the worst especially when driving and you come out of say the Blackwall Tunnel and are faced with glaring sunlight.
When I was a kid I used to tell the doctor that I was "allergic" to bright light and that it made me sneeze and he thought I was nuts. This is because it is not commonly known about to people other than those who suffer from it.
Every optician I've ever seen has not heard of it either. I explain it to them and they give me a kind of "bless the loony" smile. Then they start shining bright lights in my eyes and I sneeze three or four time in repetition and they go off and look it up online.