Final answer:
In the Harry Potter series, Snape is derogatorily referred to as "Overgrown bat" due to his dark appearance and mysterious demeanor. Other names like "Ugly git" and "Slimeball" are not specifically used for Snape in the texts.
Step-by-step explanation:
In the Harry Potter books, Professor Severus Snape has been called various derogatory names by the characters. One of the names he is referred to is "Overgrown bat", which highlights his typical black garments and sweeping cloak resembling the wings of a bat. This nickname conveys both his physical appearance and the mysterious aura he carries within the halls of Hogwarts. As for the other names provided in the question, such as "Ugly git" and "Slimeball", while they are in line with the kind of language J.K. Rowling uses to illustrate animosity between characters, it is "Overgrown bat" that we can definitely attribute to Snape. It's a term that encapsulates the essence of his intimidating and somewhat dark presence as perceived by the students.