Today I found that the "worst" question (most downvoted) on Stack Overflow is Learning to write a compiler.
Is there a good way to find the "worst" answer?
There's no way to search for answers (in this way) right now.
You'll have to download the latest data-dump, or use a data-dump sandbox like StackQL to analyze the underlying data. This answer looks like it has roughly what you need as far as a query goes, but the results in the answer are out of date.
In the time since Jon Seigel's answer was written, the
is:answer search operator has been introduced.
So, you can search
is:answer, sort by votes, and go to the last page of results. Here is the search URL.
Currently, this is the most downvoted answer on Stack Overflow: https://stackoverflow.com/questions/64242/rhino-mocks-typemock-moq-or-nmock-which-one-do-you-use-and-why/64278#64278
Though I wouldn't say it follows that the linked answer is the "worst" answer.