Meaning: a joke that does not amuse anyone.
Kim said, “Don’t play the fool all the time Peter. Your jokes are not funny and they fall flat most of the time. There is a time to be serious and a time to play the fool. All time is not fun time. Why don’t you help me with the chores instead of cracking such stupid jokes? They don’t make me laugh, they irritate me!”
Peter wondered why her mother was so annoyed.