Sexism should be inexcusable, and the dominance games that Nila mentions belong in a troop of monkeys. In the physical sciences and engineering, however, "male student egomaniacs" are extremely common, even when the instructor does fit the "traditional" professor profile, of being a tall, white, hetero male with a loud, American-accented voice, like me. What's the matter, haven't you ever seen the TV show, "The Big Bang Theory?" The real world is more up to date than the show, however: females of this obnoxious species are becoming increasingly common in my physics classes. I'm not so sure we should consider this "progress," of course: it would be better if all of them had good manners.
Harold Urey, a Nobel prize-winner in chemistry at the U. of Chicago in the '50s, used to call this "the Old Gunfighter Syndrome." By this, he meant that if one of these students could prove him wrong about anything, no matter how trivial, it would be perceived (it's unclear by whom) that all the Nobel laureate's prestige would fall onto the student. Urey said this was annoying, but it could be useful, for getting these students to work on interesting problems---or to read the textbook, as I often encourage mine to do.
Students like this try my patience too, but remember that both Albert Einstein and Thomas Edison were booted out of school for asking their teachers too many questions they couldn't answer. Sometimes, if they have any substance and what they do isn't wholly posturing, students like this can help you: if they really are as good as they think they are, your class notes will be thoroughly proofread after they're through with your classes.
They sure beat the lazy, dead-eyed, mouth-breathers we so often complain about!
