Green’s Dictionary of Slang

(US campus) an ostracized student.

1942

A.B. Hollingshead Elmtown’s Youth (2007) 221: ‘Grubbies’ are set off from the other students for many reasons [...] Boys and girls identified as grubbies are ‘nobody’ in the eyes of non-grubbies. To be rated a grubby is comparable to being blacklisted.