The party was held during a meeting of the Grand Order of the Water Rats, an exclusive club for vaudevillians, of which Chaplin had been a member since 1931. In fact, Russell officiated Chaplin's initiation ceremony (read more about it here). Only three weeks before this gathering the U.S. government revoked Chaplin's reentry permit while he was sailing to England with his family aboard the Queen Elizabeth. It is clear from the tone of his speech that he was still bitter.
Watch other (silent) clips of Chaplin from this event here and here.