Banned items are marked in NEI/JEI with a tooltip of "Deactivated" or "Deactivated by GrumpyCraft" in order to distinguish them from other tooltips using the word deactivated. Simply searching the word "Deactivated" in NEI/JEI will return the banned items for the server.
Why are Certain Items Banned?
Items are banned due to bypassing PVP, grief prevention measures, duplication glitches, or negative impact to server performance. We attempt to find code fixes for items to ensure we do not have to ban them, but that is not always possible or practical.
I Want An Item Unbanned
We typically do not unban items which have been banned. We will consider a ticket logged to request an unban under the following circumstances:
You have found a fix for the reason the item was banned.
You can show that this item does not have a reason to be banned anymore (e.g. due to pack update or changing circumstances)