New bug means: British public school slang for a new pupil - a first-year student or recent arrival at a boarding school. 'Bug' as a term for a junior schoolboy was common in English public school vernacular of. It is informal slang, fine in casual speech but not suited to formal contexts. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. It is an education-system term, so usage is institutional and routine.