Snivellus

From UnknowableWiki

Snivellus is a derogatory nickname given to Snape by James Potter and Sirius Black upon their first meeting aboard the Hogwarts Express (DH33). James and Sirius use it to refer to Snape during their confrontation after the Defense Against the Dark Arts OWL.

That same afternoon, after Snape calls Lily Evans a Mudblood, she retorts by referring to him as Snivellus; the incident signals the end of their frienship (OP28).

Twenty years later, when Snape mocks Sirius for not doing real, useful work for Order of the Phoenix, Sirius uses the old Marauder nickname for Severus, stating that he—unlike Dumbledore—does not trust Snape's change of heart (OP24).