Sienna Syndrome is a type of syndrome where you have a crush on a girl. Once you do, you forget she is in your presence and start acting goofy, inappropriate (as a joke), and weird in front of your friends which makes you laugh. Your crush gets weirded out and there is never a chance for a second impression, though you can still come close to her if you are somewhat of her type and improve. Not guaranteed though. Men, be careful! It may be uncurable if you aren't careful and do it for long periods of time without knowing she doesn't like you for a while.
Me: *acts weird in front of friends and makes them laugh and say something just as weird back*
Crush: -in the distance- Wow, he is kind of weird. I'm going to try and avoid him.
3 MONTHS LATER...
Me: Hey -----!
Crush: Oh it's him.. Hi.
Me: *walks away* How can I make her mine?? It is so weird how she is acting
GOD: The irony is crazy! >:) He definitely has Sienna Syndrome.