"He regularly stabs, mangles, perforates, burns, and otherwise damages your precious character. He delights in torturing your PC's emotions, thwarting their every plan, denying every desire. And you love your GM for just these things and more!" (Source: EnWorld)
As a bit of fun I suggest you check out You Know your GM's Evil When on the excellent blog GeekNative. It compiles nearly 4 years worth of suggestions from the popular poll of the same name from the GameWyrd website (the predecessor to GeekNative). I'm pretty sure you can find something from that list that makes you think of your GM. Bless em.
To celebrate the day, many publishers and online retailers are offering discounts. For details check out the ENWorld news page.
Mr Evil GM sir, I Salute You.