I guess I'm just lucky then. The Creative Writing class that I'm currently in is all about improving your writing method, not about writing for literary snobs. Near half of the stories in the class turned out to be fantasy styled stories, as was mine.
However, since your class frowns on the supernatural, how about a story about a man's spiral into madness? He sees things that he believes are supernatural, but they turn out to be figments of his imagination... or do they?
Or you could write a semi-historical story. Perhaps, a story set during the Hundred Years War, but from the perspective of a lowly man-at-arms. Or something of that nature.
Perhaps do a college story with a twist. The main character is your average every-day college student, outgoing, kind, has a good girlfriend, etc. However, on this one day he ends up making all the wrong choices and quickly spirals downward into a character that is hateful and loathing and generally unlikeable. Perhaps he heads off to a rather rowdy party where he ends up cheating on his girlfriend, one of his friends gets too drunk and passes out and dies. However, instead of taking him to the hospital, he decides to dispose of the body and it all goes downhill from there.