That feeling after you argued with the support of some service and they finally admit their api is broken!

I'm not sure why, but poorly written APIs anger me even more than poorly written code you inherit. And poor documentation (i.e. <SomeField>string</SomeField> with no description of what it can or can't contain, what its point is or example data!) is just as infuriating!

I have encountered vendors guilty of all of the above. It is sad and frustrating.