nice

• Not being articulate enough
• No example code
• Not building for the entire tech stack. For example, some APIs have only XML format, no JSON

1. Missing Examples - I have seen this too many times.
2. Inconsistency - naming inconsistency, result inconsistency, description inconsistency.
3. Not notifying about API changes - I've been in this situation several times and let me tell you, it's not beautiful.

This is in terms of what is bad documentation and not architecture of the APIs per say (that is a whole other discussion!)

1. Missing example implementation
2. Missing error cases/scenarios. And no proper error redressal steps.
3. Improper organisation of the APIs. There has to be a logical way of listing your APIs, so that its intuitive to look for a particular one.

I will go for a REST-API.

• missing curl / request examples
• missing sandbox
• missing consistency in naming or behaviour

Indirect answer, but I hate very complex API structures with not very meaningful naming. An API should almost be self explaining.

I also hate XML APIs.

To your question: I hate inconsistency.