I'm not sure what bar you're looking for regarding bad software design, but I remember a wonderful blog post by the Pinterest team discussing how they solved some database issues created from the birth of their service.
Additionally, reddit has notoriously been rewritten three or four times now and their dev blog may have some insight into that.
Are you looking for just genuinely terrible software design that still exists in the wild? Or examples of failed software companies? Something else?
Depending on the answer a lot of what you're looking for may be subjective.
I am looking for bad architecture in existing/recently existed in software/web applications. I want to do a case study for software architecture and design module that I am taking.
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.