A Sinse belongs to one of the lesser groups in school and usually has no friends. These are the people that you know sit in the back of the classroom plotting to kill everyone! They don't belong to any group, and they usually have a single style. They will wear the same clothes or something of the sort almost everyday. Sinse is an accronym for Single Individual Needing Social Experiece.
Matt: How was Math?
Aaron: It was cool but that sinse kid scares the s**t out of me..