Mine's pretty obvious in meaning, a half-wit is a synonym for an idiot. I chose it when playing WoW back in BC, on the heels of having far-too-serious of a time in my life. The self-deprecation led to what felt to be a more approachable persona, and definitely helped to break the ice more than once. There's also been people that have written me off at the outset from the name alone - but I consider that a benefit :p