Salesforce. Although I wasn't involved in the purchase or the implementation, I spent many 100 hour weeks dealing with the crapshoot of an implementation. A large company abused that software to the point of no return. They used that thing for everything, and then they didn't even use it right for the one thing salesforce is good at. So I guess I don't have anything against salesforce itself besides its scalability issues, custom SOQL syntax, user model, and pricing. I'm more upset about the salesforce developers/business owners that decided it was okay to use salesforce for things it was never meant for, like inventory, project management, 3rd party sales team, and so many other things that caused what should have been sub-second queries to take 30 to 60 seconds.