1. Some guy
Originated from Ken Griffey, Jr. Baseball for Super Nintendo. Making a team from scratch can often be a tedious and arduos task. Trying to come up with names to fill your entire roster is boring and stupid. So, to speed up the process, players like "Some Guy" tend to make the team. Since we are talking 16-bit, the game cuts off the first name and replaces it with the first letter. Hence, S. Guy.
2. A male who acts out of place.
Sometimes shortened to "an s"
2. Stop being an s.