Do you mean via the API, or via the Twitter website and apps?
In the case of the apps and website, you can report accounts by using the “Block or report” option, and using the “File a report” option inside that to mark a tweet as having sensitive content.
On the API, we have a report spam endpoint, but other actions are currently restricted to the use of Twitter client apps.
For more information on these issues please see our Support pages on this topic.