A joker in dreams is a free spirit or a self-actualized personality, one who has come to terms with life on the physical plane of existence.
Psychological / emotional perspective: Emotionally, a joke can bring about a release of tension and a bizarre occurrence in dreams which causes amusement can do the same.
The aspect of our personality which shows itself as a joker has the same meaning as a jester – someone who can make us laugh at ourselves and arouse a sense of the ridiculous.
Material aspects: A joke in dreams can be an image presented in an odd way. It is as though the mind develops the oddity in order to have us remember what it is attempting to present.