Place it at the exact end of the failed joke as the closing reaction, then follow it with the Sad Violin Sound Button if the moment needs a mock-tragic fall, or with Nelson's Ha-Ha! Sound Button when the group starts laughing at the failure instead.
About this sound
A short 2.8-second voice clip of a man flatly saying 'not fucking funny mate' in a blunt, exasperated tone. The delivery is dry and dismissive rather than shouted, which makes it feel like an instant put-down for a joke that fell flat. It lands as awkward, mildly annoyed and funny in its own deadpan way.