How to tell if someone told a good joke?
You can tell if someone said a good joke if it makes a person laugh or giggle after it was communicated.  You can also tell if a good joke was said by an audience reaction to the joke, if they cheer, or if they boo.  Booing is a sign the joke was not so good, and cheering is a sign the joke was good.  A reaction of silence to a joke means the joke was not understood.  If you or an audience don't understand the context of joke make sure to ask for clarification so you can take part in cheering or booing depending on how you respond to it.