Hi,
Couchbase Server hasn’t released a version that supports Mac OS X Sierra 10.12 yet. That might be your issue.
The other thing is that to uninstall, you need to delete the directories where Couchbase Server stores logs and data to disk. You might not have both directories, depending on the types of buckets you’ve enabled.
rm -rf ~/Library/Application\ Support/Couchbase
rm -rf ~/Library/Application\ Support/Membase
-Will