That one product you want to go back
What is that one product/tool/API/topic that you hated and do not like to go back or think about if somebody asks you.
In one of my projects at McGraw-Hill, I was supposed to work on .NET but was given some VBA work. I had no idea how to work with non-OOPs classes. I did it but it was probably one of the project, I did not like at all. If somebody asks me today, I say, I do not know VBA.
Another product I hate is Crystal Reports. One of the worst product I have ever worked with. Too many bugs and problem. No body knows how to resolve them. Bad product support.