Ask HN: How do you deal with a bad API?

Right now I'm coding against a bad API. Spotty docs. No test environment. Ungroomed data. Many behaviors impossible to predict until real users in particular populations or situations turn up and do real-user things.

I have a bag of tricks that is working well enough for me. But I figure many HNers must have other good tricks and API war stories. So I'll ask: What bad APIs have you dealt with, and how have you kept your code and your team sane despite that?