Worst practices in Django you have ever seen
Monkeying around with pre-save and post-save events.
If you can't simply do it in save, you should probably rethink what you're trying to do.  After all, it's just a relational database under the hood.  If what you're doing gets too complex, you'll have ORM mapping issues.
Trying to write uber-generic -- one view does it all -- functionality.  View functions are  functions for a reason.  They can use modules, packages, objects, other functions, etc.  They can be short and similar without it being a code smell. 
If you need to use 10 lines of code to construct the uber-generic-do-it-all object and it would have been a 12-line view function without the uber-generic-do-it-all object, then the uber-object isn't helping.
Imposing too much super-sophisticated object class design on the ORM model classes.  If it requires abstract base classes or metaclasses, it won't do well in the ORM layer. 
Failing to make use of tests.py and the test client to create complete unit tests of whatever it's claimed that the application does.
What are the worst mistakes made using Django framework, that you have noticed? Have you seen some real misuses, that maybe should go as warnings to the Django docs?