While humor in everyday conversation has been acknowledged widely as an area of linguistic research, failed humor has not received much linguistic attention. This paper describes unperceived humor and rejected humor, analyzing several examples from a conversational corpus using the double voicing approach according to Bakhtin. Unperceived humor can quickly lead to misunderstandings such as a joke being understood as a verbal attack. Rejected humor, on the other hand, is perceived but purposely ignored by one or several of the listeners, for instance in order to continue the discourse as planned. In both cases, the difference in mode of speech (bona fide communication versus non-serious communication) can be considered a major reason for the failure of humor.