Keep your sense of humor, my friend; if you don't have a sense of humor it just isn't funny anymore.

This quote means that it is important to be able to laugh at yourself and not take things too seriously. It suggests that if you don’t have the ability to laugh at yourself and make jokes about life, it will be hard to find humor in any situation because it won’t be as funny. This quote is encouraging an individual to keep a sense of humor, so that life can be more enjoyable and humorous.