Kang didn’t reveal the context, but I’m imagining Negan either whacking somebody in the face with it or flinging the contents at somebody.
Interestingly, Angela Kang’s comments to The Huffington Post do indicate that the Walking Dead production team has put some thought into how Negan’s bathroom situation works.
That said, maybe it could be as simple as Michonne or somebody else confiscating the pan for some reason.
Apparently, his bed pan/bucket will have a part to play later in Season 9.