Answer:
Sid Vicious's real name is John Ritchie. Since he lived with a few other Johnnys, it was inevitable that he would get a nickname.
Sid doesn't stand for anything. It was a name given to him by his roommates, one of them being Johnny 'Rotten' Lydon. Rotten had a hampster that was really cute named Sid, and one day it attacked his finger; he cried out "Sid is so vicious!" Some time later, Ritchie- who was known amongst his friends for being quiet and rather calm- got in a fight with a Bouncer and was kicked out of a bar. His friends were so surprised that quiet Johnny Ritchie spazzed out that they renamed his Sid Vicious. He took it as his stage name when the Sex Pistols formed.