Bad Slash is defined as "improbable or poorly-written romantic encounters between characters of the same sex." Bad slash is a separate category because many of its badfic traits are less likely to afflict non-slashers. These traits include constant pronoun confusion ('The Pronoun Problem') (e.g., when two characters of the same sex sleep together and the readers don't know which "he" the author means), character neutering (wherein a character who is canonically masculine suddenly acquires the personality of a Harlequin romance novel heroine), and mpreg (e.g., Faramir finds out that he is pregnant with Frodo's baby). These problems stem mostly from the fact that the majority of Bad Slashers write relations between two homosexual adult males but are themselves heterosexual adolescent females who don't feel like doing a lot of research.
Bad biology is also frequently found in bad slash; mostly because, as observed above, the authors don't feel like doing a lot of research. Without wishing to go into details, often what occurs in bad slashfics would cause pain to or internally injure a character, or is simply not possible. It's not that we advocate underage slash authors researching the exact mechanics of gay sex, it's just that we'd like to not have to take so many canon characters to Medical. So if you don't know what's involved when two guys are gettin' it on, then kindly don't write about it.
Since there is not always a Mary Sue in Bad Slash, the slash demons are exorcised from the canon characters by way of banging the characters on the head with a copy of canon.
It is probably worth noting that we in the PPC fully believe in and acknowledge the existance of good slash. Hence 'Department of Bad Slash', rather than simply 'Department of Slash'.
See also the Department of Bad Slash.