When someone gets a 98% score and complains about it, what do you call them?
In American English this kind of person, one who is close to perfect but not quite and seeks those extra points, is called a
They are complaining in order to get those few extra points that, to everyone else, they don't really seem to need. It is a very light pejorative.
I would call a person who scores 98% on a test and complains about it a Type A personality. From Wikipedia:
Type A and Type B personality hypothesis describes two contrasting personality types. In this hypothesis, personalities that are more competitive, highly organized, ambitious, impatient, highly aware of time management and/or aggressive are labeled Type A, while more relaxed, less 'neurotic', 'frantic', 'explainable', personalities are labeled Type B.
The complaint arises mostly from a combination of (1) competitiveness, and (2) ambition with the high degree of organization required to achieve that ambition. While our someone may have scored 98%, members in her "peer group" may have scored higher. From her perspective, not good. Also, the ambition was to score 100%, not 98%. Not good enough.