One of the many things Leonardo da Vinci was famous for was writing his notes backwards. There's a lot of speculation about why he would do that but even without knowing, it's a neat little parlour trick that anyone can learn.
This video from David Meyer demonstrates the simple, yet sinister, trick behind writing backwards.
All you need to do is use your off-hand to mirror the actions of your dominant hand as you write.
For right-handed people, this is where the trick becomes slightly sinister (although not in a way that would qualify this for Evil Week) and left-handed people get the joy of even more ink smudging.
With practice, you'll build up the fine motor skills for your writing to be legible and you too can write like da Vinci. Even without practice it's a silly little way to show off.