Okay, so the reason I ask this question is because it comes up a lot when talking to different engineering majors at my school. The common consensus is that the hardest engineering degrees are mechanical and aerospace with chemical, electrical, and computer engineering in second, and civil and environmental in last (my school doesn't offer industrial or any of the other ones).
Among the life sciences category that also includes anatomy, neuroscience, and genetics, biology tops the list of “hardest” majors with one of the lowest average GPAs. Graduates of a biology program may go on to pursue careers in medicine, dentistry, or veterinary sciences.
What about liberal arts majors? anything that's not a joke? maybe philo? or poli sci? econ is a joke, but i think the really really advanced areas are pretty challenging, but there are so many dumbasses majoring in econ, so basically no.