I'm sick of good fanfictions being ruined by Mary Sues. Don't know what a Mary Sue or her male counterpart, Gary Stu is? 

Via en.wikipedia.org:

"A Mary Sue (sometimes just Sue), in literary criticism and particularly in fanfiction, is a fictional character with overly idealized and hackneyed mannerisms, lacking noteworthy flaws, and primarily functioning as a wish-fulfilment fantasy for the author or reader. It is generally accepted as a character whose positive aspects overwhelm their other traits until they become one-dimensional. While the label "Mary Sue" itself originates from a parody of this type of character, most characters labelled "Mary Sues" by readers are not intended by authors as such. Male Mary Sues are often dubbed "Gary Stu", "Larry Stu", "Marty Stu", or similar names"

Fill out my Mary Sue (for Harry Potter) form and see if your OC falls into this horrifying category!