How can I quickly remove an item that should not be active in the catalog?

There are two options to remove an item. Within the Customer Dashboard, go to the "Indexes" tab and click "Products." Search for the item in question and use the trash icon on the far right to remove the particular item.

There is also the option to deactivate an item via the API. This can be done using the CSV catalog API or Items API.

When the item is added back to the catalog or reactivated, all of the learnings are retained for future use.