Ho ho ho, these guys (arrogant classmates that is). What I find, is that these people are actually trying to hide whatever failings they have by intimidating or impressing others (putting on my fake psychologist hat here). There was this one guy in my class this year (and was in my class this year,

) who had the most obnoxious voice (think super arrogant nerd voice in any teen movie) and would always answer questions of the professor - often it was completely unrelated or worse: he wouldn't wouldn't even answer the question - he would ask a question of his own and then answer it himself (you know, to show of his "superior knowledge)!
The thing is, if I can detect his BS, of course the prof certainly can (so I have that to comfort me); what got me was that other classmates thought he was Mr. Knowledgeable! But whenever I heard him talk to his closer friends about exams and such, he would be saying something like "hoping for a 50% on this one..." I recall we needed 40% on this exam, so I joked to my friends, thinking, "ooh, he's shooting high this time!" There were (are) others like him, just less of an extreme case.
But on the other hand, I am guilty of sleeping in class and other such non-lecture worthy activities. For first year bio and chem (mandatory), me and my friends, despite sitting at the
front of the class, would whisper, silently hi-five each other, do the crossword, or sleep. And lots of other classmates resented us a bit when seeing that, since we were (sorry about this) near the top grades-wise.
What you have to keep in mind is that those people are there
just in case the prof says something not in the textbook that could be on the exam (which happened a lot last year). Not to mention, physics 100 is required anywhere and everywhere no matter who you are, and even those lazy geniuses still want to get a good mark!