Not the worst, but deserves a mention due to how common it is.

Say your whatever object has a method called Configure. You can infer a lot from the configuration parameters or type that it takes, but for whatever reason something is unclear or doesn't work.

Tooltip from xml comments: Sets the configuration.
Official guide: Sets the configuration <br />.
Technical API reference: Sets the configuration.

I would create a support ticket explaining how this is unclear if I wasn't half expecting the suggested solution to be "you know what I mean".