A classhole is a rare breed of student, the kind who insists upon commenting upon absolutely everything the professor says, even if his/her comment is as meaningless as nodding and verbally giving his assent/dissent. The classhole also answers just about every question asked, even when everyone else is sick to death of hearing him/her spew their insignificant opinions about topics nobody really cares about in the first place. Class is a time to shut your mouth and listen to the professor, who has years of education and probably four or five different diplomas to boot; the knowledge of the classhole pales in comparison, but this is a fact that is only evident to everyone else in the class. The classhole, so smitten with themselves, remains ignorant.
The foreign exchange student who nods his head every time the professor says something "meaningful" and voices his opinion every damn chance he gets is undoubtedly a classhole.