They are a blight on the multiverse. They are the end result of decades of neglect by those who should know better. They are an eyesore, an atrocity, a- sorry, what's that? What are they? Oh.
A Sueniversity is a fanfiction written along the lines of the Official Fanfiction University of Middle-earth. However, unlike the many authorised spinoffs - those which were specifically authorised by Miss Cam, and those which follow in her footsteps - these Sueniversities do not promote goodfic over bad. They do not encourage Learning Through Pain. They do not put a stop to fangirlish activities.
In short, a Sueniversity is a Fanfiction University - with all the hallmarks of the OFU brand, such as lessons taught by canon characters, cruelty to students, etc etc - which... doesn't do its job. It's badly written, it lets the fangirls run riot, the canons are out of character - you get the gist.
No more. The problem has been recognised at last, and it will be addressed. Those who know the most about creating OFUs - the Course Coordinators of Miss Cam's heirs - have banded together to form the Official Fanfiction University of Official Fanfiction Universities.
OFU2 is here. Prepare to learn.