It derivates from the name Mitya.
My real name is Dima. The both names are close in Russian culture. All my close friends calls me - Mitya.
One of my friends was joking over my name and called me "Miting" [Meeteeng]. It's literally meaning "a rally" in Russian. So it was a joke over me.
When I needed a nickname longer than Mity/Mitys, I started to use Miting in 2007, I guess