cuckoo in the nest
Someone in a group who is seen as different and ostracized by their peers. Since Sam always got good grades and never got in trouble, he was seen by his unruly peers as a cuckoo in the nest.
cuckoo in the nest
an unwelcome intruder in a place or situation. The female cuckoo often lays its eggs in other birds' nests. Once hatched, the cuckoo fledgling pushes the other birds' fledglings out of the nest.