By drawing on methods used in conversation analysis and interactional linguistics this article discusses the interplay between grammar and social interaction. It investigates a reduplicate linguistic item in Finnish called the `joke-joke' structure. It is shown that the structure is used in interactional sequences in which some prior turn can be understood to be ambiguous in meaning and to have been produced either seriously or non-seriously. Speakers use the `joke-joke' structure, as a kind of metacomment, to shift from an implied serious stance to a non-serious position. In essence, they use the structure to recontextualize and make the prior position ambiguous retroactively. It can thus be considered as a specific form of repair. The structure predominantly occurs in teasing and overstatements. The use of the structure can be seen to reflect the participants' mutual understanding of sociocultural values. The use of the reduplicate structure can also be seen to be functionally motivated: it can be produced quickly and it iconically intensifies the meaning of `joking'. The findings here also support previous findings that reduplicates are frequently used to display emotional states. Finally, this article shows that meanings and understandings frequently emerge and are negotiated in social interaction.