fall flat
1. To fail or be ineffective. Good luck—the last time management tried to implement a new dress code, that measure fell flat. I can't believe the vote fell flat—I really thought we had enough support in Congress this time. No wonder your threats fall flat—you never actually punish the kids for their bad behavior.
2. To fail to be humorous, as of a joke. A: "Unfortunately, my first stand-up routine really fell flat." B: "Well, maybe you just had the wrong audience." Did you hear me? I said, "Orange you glad to see me." OK, wow, that joke fell flat. Great-Aunt Shirley has no sense of humor, so don't discouraged if your colorful stories fall flat with her.
Farlex Dictionary of Idioms. © 2024 Farlex, Inc, all rights reserved.
fall flat
Fail, prove to be ineffective, as in His jokes nearly always fell flat-no one ever laughed at them. [First half of 1800s] 
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
fall flat
 COMMON
1. If an event or an attempt to do something falls flat, it is completely unsuccessful. If the efforts fall flat and the economic situation does not change, this city can expect another riot 25 years from now. She was badly disappointed when the evening fell flat.
2. If a joke falls flat, nobody thinks it is funny. He then started trying to tell jokes to the assembled gathering. These too fell flat.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012
fall flat
 fail completely to produce the intended or expected effect.Farlex Partner Idioms Dictionary © Farlex 2017
fall ˈflat
 if a joke, a story, or an event falls flat, it completely fails to amuse people or to have the effect that was intended: I didn’t think the comedian was funny at all — most of his jokes fell completely flat.Farlex Partner Idioms Dictionary © Farlex 2017
 fall flat
1.  To fail miserably when attempting to achieve a result.
2.  To have no effect: The jokes fell flat.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.