In this article, we investigate social meaning as a determinant of linguistic diffusion by confronting laboratory and corpus data of Citétaal, a multi-ethnolect that has spread across Flanders. In a speaker evaluation experiment, we found that Citétaal was upgraded on ‘streetwise dynamism’, even by respondents unfamiliar with its migrant origin. From this, we conclude that it is Citétaal's third-order indexicality, pruned of ethnic associations, which carries the diffusion. To determine the relative importance of streetwise cool vis-à-vis other predictors, we studied the diffusion across Twitter of the principal Citétaal shibboleth (/s/ palatalisation). As a production proxy for streetwise cool, we included expressive compensation strategies such as lengthening (verrry), which turned out to be among the main predictors of the Citétaal form. We argue that social meaning is a major change determinant, and that Twitter is the optimum source to track both a diffusion and the factors, including social meaning, which drive it. (Rapid linguistic diffusion, social meaning, streetwise prestige, speaker evaluation experiment, corpus linguistics, Twitter)*