Gay parents...pretty legit reason. There's also the old "I glued my pencil to my non-writing hand", the "I jacked my fingers up so badly that I can no longer grip a pencil" and the hipster "I wrote with my left hand, even though I'm right-handed, BEFORE it was cool". It's also a nice party trick and I hear that if you do it at a bar they will give you a fresh bowl of nuts, so you don't have to eat from the piss-covered ones.