As well as the automated unsubscribe features, you can also unsubscribe a specific email address or set of email addresses. If you want to unsubscribe an individual, you can type just that email address exactly as it's written and hit "find" to unsubscribe them. This will not delete them from your data base, it will move them from your Active Mailing List to your Unsubscribed List (inactive.) 

Other Options: If you have a member record that needs to be unsubscribed from all your lists, you can do a "global unsubscribe" from your Account Management page. You can also create a blacklist, which prevents certain emails from receiving messages but does not remove them from your active list.