the more important issue for your problem statement is that the Disallow syntax matches the url path left-to-right.
therefore if you want to take advantage of REP extensions to pattern matching you can disallow a url ending with "feed" using: Disallow: /*feed$
however if you also/instead want to disallow a "feed" subdirectory url (i.e. ending with "feed/") you need a different rule: Disallow: /*feed/$
also note that without the end anchor in the pattern (the "$") you will match more than intended, such that disallowing the pattern "/*feed" will disallow urls such as "/feedme" and disallowing the pattern "/*feed/" will disallow urls such as "/feed/me"