My last name is Smith and when you have a generic name like "Mike Smith" you need some kind of identity. When I started college I worked at a place that had 5 Mikes and it was utter confusion when someone would call and say "I spoke to Mike". One of my co-workers started calling me Smitty and it stuck. Several years later I started my professional career and I worked as a afternoon drive DJ on a country radio station. Guess what name I went by on-air? Smitty!
I've lived in the Sacramento area for over 10 years so I added "sac" in front of it.